CN106301053A - Three-phase four-leg inverter control method under the conditions of imbalance, nonlinear load - Google Patents

Abstract

The present invention provides a method for controlling a three-phase four-leg inverter under unbalanced and nonlinear load conditions, including step 1, sampling the three-phase output voltage amplitude, phase and frequency of the three-phase four-leg inverter in real time, After decomposing and processing, the decoupling control is realized through abc/dq0 coordinate transformation; step 2, combined with repetitive control technology and PI control technology, respectively perform closed-loop control on the d, q, and 0 axes to achieve the control goal; step 3, in dq0/ After the abc coordinate transformation, the three-dimensional space vector modulation technology based on the abc coordinate system is used to realize the trigger control of the four bridge arms of the three-phase four-leg inverter. The invention solves the problems of unbalanced and non-linear loads in the distribution network, which cause the three-phase output voltage asymmetry and waveform distortion of the inverter, and realizes the three-phase four-leg inverter under unbalanced and non-linear load conditions. The output voltage is symmetrically output, and at the same time, the DC component and harmonic component are effectively suppressed.

Description

Three-phase four-leg inverter control method under unbalanced and nonlinear load conditions

technical field

The invention relates to the technical field of power transmission and distribution, in particular to a control method for a three-phase four-leg inverter under unbalanced and nonlinear load conditions.

Background technique

In recent years, my country has vigorously developed distributed power generation, including new energy, to meet the needs of global economic development and the dilemma of increasing energy scarcity. At present, in the power system, the inverter has become an indispensable part of the power system. As the core component of the energy conversion and control process of the distributed power generation system, it affects and determines the stability, safety, reliability and reliability of the entire system. Efficiency, and even service life and cost, have become the key to the development and application of distributed generation.

But at the same time, there are a large number of unbalanced and nonlinear loads on the user side and the grid side in the distribution network, and they are increasing day by day. The unbalanced load will cause the asymmetry of the three-phase output voltage of the inverter, which is the main reason for the asymmetry of the three-phase output in the power system, while the nonlinear load will cause the inverter output waveform to be distorted and generate a large amount of DC components , Harmonic components, deteriorating power quality. Because the traditional three-phase three-leg inverter is limited by its own topology, it cannot control the potential relationship between the midpoint of its filter capacitor and the midpoint of the DC bus voltage, and it does not have the ability to carry unbalanced loads. Therefore, in recent years, unbalanced , Three-phase inverter control technology research under nonlinear load conditions has received extensive attention.

Contents of the invention

The purpose of the present invention is to propose a three-phase four-leg inverter control method under unbalanced and nonlinear load conditions to solve the asymmetry of the three-phase output voltage of the inverter caused by unbalanced and nonlinear loads in the distribution network , Waveform distortion problem, realize the symmetrical output of the three-phase output voltage of the three-phase four-leg inverter under unbalanced and nonlinear load conditions, and effectively suppress the DC component and harmonic component.

The purpose of the present invention is achieved by the following technical solutions:

A method for controlling a three-phase four-leg inverter under unbalanced and nonlinear load conditions, comprising the following steps:

Step 1. Real-time sampling of the three-phase four-leg inverter three-phase output voltage amplitude, phase, and frequency, and decoupling control of it through abc/dq0 coordinate transformation after decomposition;

Step 2. Combining repetitive control technology and PI control technology to perform closed-loop control on the d, q, and 0 axes respectively to achieve the control goal;

Step 3: After the dq0/abc coordinate transformation, the three-dimensional space vector modulation technology based on the abc coordinate system is used to realize the trigger control of the four bridge arms of the three-phase four-leg inverter.

Further, the specific implementation process of the first step is as follows:

a) Real-time sampling of the three-phase four-leg inverter three-phase output voltage amplitude, phase, and the three-phase output voltage Decomposed into positive sequence, negative sequence, zero sequence voltage components:

${\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

${\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; =</span>{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

${\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The subscripts (1), (2), and (0) in formulas (1) to (3) represent positive sequence, negative sequence, and zero sequence components respectively;

b) The positive sequence, negative sequence, and zero sequence components obtained by decomposing the three-phase four-leg inverter three-phase output voltage are respectively subjected to Park transformation to realize decoupling control:

Further, the second step combines repetitive control technology and PI control technology to perform closed-loop control on the d, q, and 0 axes respectively, so that the d-axis voltage component control target is 220√2V, and the q-axis and 0-axis voltage component control targets are 0V ,

Among them, in terms of repetitive control, the output deviation is calculated by comparing the sampling value at a certain moment in the previous power frequency cycle with the control target, and the deviation obtained by comparing it with the corresponding time in this power frequency cycle is accumulated and used as the feedback amount of the controlled object. And continue to apply the accumulated value to the next cycle, repeating the cycle;

In terms of PI control, the output deviation is calculated by comparing the sampling value obtained by sampling with the carrier cycle as the unit with the control target, and it is directly used as the feedback amount of the controlled object.

The present invention proposes a three-phase four-leg inverter control method under unbalanced and non-linear load conditions by using the three-phase four-leg inverter and utilizing its characteristics that the three-phase voltage outputs are independent of each other. It solves the three-phase voltage asymmetry and waveform distortion problems caused by unbalanced and nonlinear loads in the distribution network, and meets the current increasing demand for three-phase inverters with unbalanced and nonlinear loads.

Description of drawings

Figure 1 is a schematic diagram of the topology of a three-phase four-leg inverter;

Fig. 2 is a control principle block diagram of the three-phase four-leg inverter control method under unbalanced and nonlinear load conditions of the present invention;

Fig. 3 is the basic principle block diagram of repetitive control among the present invention;

FIG. 4 is a simulation waveform diagram of three-phase output voltage of a three-phase four-leg inverter under unbalanced and nonlinear load conditions in the present invention.

detailed description

The technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the present invention.

Please refer to FIG. 1 and FIG. 2. The present invention provides a method for controlling a three-phase four-leg inverter under unbalanced and nonlinear load conditions, including the following steps:

Step 1: Sampling the three-phase four-leg inverter three-phase output voltage amplitude, phase, and frequency in real time, decoupling and controlling it through abc/dq0 coordinate transformation after decomposing and processing.

The concrete realization process of described step 1 is as follows:

a) Real-time sampling of the three-phase four-leg inverter three-phase output voltage amplitude, phase, and the three-phase output voltage Decomposed into positive sequence, negative sequence, zero sequence voltage components:

${\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

${\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; =</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

${\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Subscripts (1), (2), and (0) in formulas (1) to (3) represent positive sequence, negative sequence, and zero sequence components, respectively.

b) The positive sequence, negative sequence, and zero sequence components obtained by decomposing the three-phase four-leg inverter three-phase output voltage are respectively subjected to Park transformation to realize decoupling control:

Analyzing formulas (4)-(6), we can see that:

1) When the three-phase load is balanced, the output voltage of the three-phase four-leg inverter has no negative-sequence and zero-sequence components, and the space vector synthesized in the dq0 coordinate system is stationary relative to the dq0 coordinate system, and on the d-axis and q-axis The component of is a certain value, and the component on the 0 axis is 0;

2) When the three-phase load is unbalanced, the positive sequence component in the output voltage of the three-phase four-leg inverter is consistent with the situation in 1); the rotation direction of the space vector synthesized by the negative sequence component in the dq plane is opposite to that of the dq0 coordinate system. The projection on the dq coordinate axis is the double frequency of the sine quantity, and the projection on the 0 axis is 0; the zero sequence component is represented by the 0 axis in the dq0 coordinate system, which is the sine quantity on the 0 axis.

3) Real-time sampling of the three-phase four-leg inverter three-phase output voltage amplitude and phase, and perform discrete Fourier transform on it:

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; \&infin;</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; n\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; n\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

In formula (7), n represents the frequency multiplication frequency of the sine quantity, and a _n and b _n (n≠0,1) are the amplitudes of the sine and cosine terms of each harmonic respectively.

Analysis formula (7) shows that:

When the three-phase load is non-linear, the output voltage of the three-phase four-leg inverter can be decomposed into fundamental wave components, DC components, and higher harmonic components.

In the dq0 coordinate system, the space vector synthesized by the fundamental component is similar to that of the three-phase load balance; the DC component and the harmonic component are projected on the dq coordinate axis as the n-1 multiple frequency of the sine quantity, and projected on the 0 axis as 0.

To sum up, the decoupling control of the three-phase output voltage of the three-phase four-leg inverter can be realized only by performing closed-loop control on the d, q, and 0 axes respectively to achieve the control target.

Step 2. Combining repetitive control technology and PI control technology to perform closed-loop control on the d, q, and 0 axes respectively to achieve the control goal.

Specifically, combined with repetitive control technology and PI control technology, the d, q, and 0 axes are respectively closed-loop controlled, so that the d-axis voltage component control target is 220√2V, and the q-axis and 0-axis voltage component control targets are 0V.

In terms of repetitive control, the output deviation is calculated by comparing the sampling value at a certain moment in the previous power frequency cycle with the control target, and the deviation calculated by comparing it with the corresponding time in the current power frequency cycle is accumulated and used as the feedback amount of the controlled object, and The accumulated value is continuously applied to the next cycle, and the cycle repeats, as shown in FIG. 3 .

In terms of PI control, the output deviation is calculated by comparing the sampling value obtained by sampling with the carrier cycle as the unit with the control target, and it is directly used as the feedback amount of the controlled object.

Step 3: After the dq0/abc coordinate transformation, the three-dimensional space vector modulation technology (3DSVM) based on the abc coordinate system is used to realize the trigger control of the four bridge arms of the three-phase four-leg inverter.

simulation analysis

In order to verify the feasibility and effectiveness of the present invention, simulation analysis is carried out based on MATLAB/Simulink.

Simulation description: Simulate unbalanced nonlinear loads, and conduct open-loop and closed-loop control experiments on three-phase four-leg inverters.

Simulation parameters: Take the load of phase a as 1kΩ, the load of phase b as 2kΩ forward half-wave load, and the load of phase c as reverse half-wave load of 2kΩ.

Simulation analysis: the simulation results are shown in Figure 4. It can be seen that before and after the open-loop and closed-loop control, the three-phase four-leg inverter three-phase output voltage waveform is rapidly approaching a sine wave from disorder, indicating that the present invention can effectively control unbalanced, Three-phase four-leg inverter three-phase output voltage under nonlinear load conditions.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any changes or substitutions that can be easily imagined by those skilled in the art within the technical scope disclosed in the present invention, All should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (3)

1. the three-phase four-leg inverter control method under the conditions of an imbalance, nonlinear load, it is characterised in that include as Lower step:

Step one, real-time sampling three-phase four-leg inverter three-phase output voltage amplitude, phase place, frequency, pass through after resolution process Abc/dq0 coordinate transform realizes the uneoupled control to it；

Step 2, combine Repetitive Control Technique and PI control technology carries out closed loop control to d, q, 0 axle respectively, reach to control mesh Mark；

Step 3, after dq0/abc coordinate transform, use three-dimensional space vector modulation technology based on abc coordinate system, it is achieved right The triggering of four brachium pontis of three-phase four-leg inverter controls.

2. the three-phase four-leg inverter control method under the conditions of imbalance as claimed in claim 1, nonlinear load, it is special Levy be described step one to implement process as follows:

A) real-time sampling three-phase four-leg inverter three-phase output voltage amplitude, phase place, and by three-phase output voltageIt is decomposed into positive sequence, negative phase-sequence, zero sequence voltage component:

${\stackrel{\&CenterDot;}{U}}_a={\stackrel{\&CenterDot;}{U}}_{a\left(1\right)}+{\stackrel{\&CenterDot;}{U}}_{a\left(2\right)}+{\stackrel{\&CenterDot;}{U}}_{a\left(0\right)}---\left(1\right)$

${\stackrel{\&CenterDot;}{U}}_b={\stackrel{\&CenterDot;}{U}}_{b\left(1\right)}+{\stackrel{\&CenterDot;}{U}}_{b\left(2\right)}+{\stackrel{\&CenterDot;}{U}}_{b\left(0\right)}---\left(2\right)$

${\stackrel{\&CenterDot;}{U}}_c={\stackrel{\&CenterDot;}{U}}_{c\left(1\right)}+{\stackrel{\&CenterDot;}{U}}_{c\left(2\right)}+{\stackrel{\&CenterDot;}{U}}_{c\left(0\right)}---\left(3\right)$

In formula (1)～(3), footnote (1), (2), (0) represent positive sequence, negative phase-sequence, zero-sequence component respectively；

B) by decomposing positive sequence that three-phase four-leg inverter three-phase output voltage obtains, negative phase-sequence, zero-sequence component carry out Park respectively Conversion, it is achieved uneoupled control:

3. the three-phase four-leg inverter control method under the conditions of imbalance as claimed in claim 1, nonlinear load, it is special Levy and be: described step 2 combines Repetitive Control Technique and PI control technology carries out closed loop control to d, q, 0 axle respectively, makes d axle It is 220 √ 2V that component of voltage controls target, and it is 0V that q axle and 0 shaft voltage component control target；

Wherein Repetitive controller aspect, compared the sampled value in a upper power frequency period moment with control target and is calculated Output bias, and moment more calculated deviation corresponding with this power frequency period add up, as the feedback of controlled device Amount, and continue to be applied to next cycle by accumulated value, move in circles；

PI control aspect, the sampled value obtained sampling in units of carrier cycle with control target and compare and be calculated output partially Difference, and directly as the feedback quantity of controlled device.