CN108964066A - The Voltage Drop and harmonic wave synchroballistic method of DVR system - Google Patents

Abstract

The invention discloses a kind of Voltage Drops of DVR system and harmonic wave synchroballistic method, by the modification of detection algorithm and the adjustment of control strategy so that DVR (dynamic electric voltage recovery device) has the dual capability for administering harmonic wave and Voltage Drop.Voltage Drop and harmonic detecting method based on instantaneous reactive power theory are used on detection algorithm, realize that single-phase voltage detects by way of being delayed 60 ° of construction two-phase voltages；Control aspect uses hybrid control strategy, will fall reference quantity and harmonic wave reference quantity merges, to generate the function that pwm pulse signal realizes DVR harmonic detecting and improvement.On the basis of meeting Voltage Drop compensation, harmonic signal can be acquired accurately, so that providing good parameter basis for compensation.It can not only realize that Voltage Drop compensates during Voltage Drop and harmonic wave synchroballistic, while harmonic wave is significantly inhibited, so that the quality of load voltage has further promotion.

Description

The Voltage Drop and Harmonic Synchronous Compensation Method of DVR System

technical field

The invention relates to the field of power quality monitoring and control, in particular to a voltage drop and harmonic synchronous compensation method for a DVR system.

Background technique

In the modern power system, the power load is constantly changing from the traditional type to the type based on power electronic technology. A variety of impact, nonlinear, fluctuating and asymmetrical loads are widely used, causing a series of power quality problems, such as voltage drop, voltage fluctuation and so on.

DVR (Dynamic Voltage Restorer) is currently the most economical and effective voltage drop compensation device. Traditional DVR, as a very representative series compensation device, can effectively change the energy distribution of the line and effectively adjust the load terminal voltage. But the number of times it occurs is limited, and the DVR is in the bypass working state most of the time, so that its utilization efficiency is not high. At the same time, the investment in the bypass circuit is large, and the technical difficulty in controlling its transition from the closed state to the disconnected state is also large, which affects the operational reliability of the overall device. In addition, the traditional method does not consider the harmonics generated when the system is working, such as the harmonics generated by the sensitive load of the DVR system and the rectifier bridge, and the harmonics generated by the nonlinear load of the actual power system. The addition of these harmonics will seriously affect the load equipment. interference.

Contents of the invention

The purpose of the present invention is to provide a voltage drop and harmonic synchronous compensation method for a DVR system.

The technical solution that realizes the object of the present invention is: a voltage drop and harmonic synchronous compensation method of a DVR system, comprising the steps:

Step 1. Perform PARK transformation on the three-phase voltage of the power grid to obtain the voltage components in the dq coordinate system;

Step 2, performing a low-pass filter on the voltage component in the dq coordinate system to extract the voltage positive sequence fundamental wave component;

Step 3. Perform dq inverse transformation on the positive sequence fundamental wave component of the voltage to obtain the sinusoidal quantity of the voltage fundamental wave, and use the phase-locked loop (PLL) technology to construct the amplitude and phase of the voltage drop;

Step 4. Perform αβ changes on the three-phase voltage of the power grid to obtain the voltage components in the αβ coordinate system;

Step 5, performing αβ-dq transformation on the voltage component in the αβ coordinate system to obtain the d and q axis components, and performing dq-αβ transformation after low-pass filtering to obtain the harmonic voltage fundamental wave amount;

Step 6. Make a difference between the fundamental wave and the system voltage to obtain the harmonic voltage, which is used as the reference voltage input to the inverter;

Step 7, constructing a drop compensation voltage and a harmonic compensation voltage according to the reference voltage and the drop voltage phase;

Step 8. Superimpose the sag compensation voltage and the harmonic compensation voltage, generate a compensation signal through a hybrid control method of feedforward control and double closed-loop feedback control, and control the power switch of the inverter to perform compensation.

Compared with the prior art, the present invention has the remarkable advantages that: on the premise of not increasing the hardware equipment, the present invention provides the inverter with the reverse of the equivalent value in the line by adding a harmonic detection link to the existing detection algorithm. Harmonic voltage is used to effectively suppress line harmonics, which not only realizes voltage drop compensation, but also further improves the quality of load voltage.

Description of drawings

FIG. 1 is a schematic structural diagram of a three-phase four-wire DVR topology system according to the present invention.

Fig. 2 is a single-phase harmonic voltage detection circuit diagram of the present invention.

Fig. 3 is a single-phase harmonic voltage detection circuit diagram of the present invention.

FIG. 4 is a schematic diagram of the voltage drop and harmonic compensation of the present invention.

FIG. 5 is a single-phase voltage drop and harmonic compensation waveform diagram of the present invention.

FIG. 6 is a waveform diagram of three-phase voltage drop and harmonic compensation according to the present invention.

FIG. 7 is a flow chart of the voltage drop and harmonic synchronous compensation method of the present invention.

Detailed ways

Three-phase four-wire system DVR topological system structure shown in Figure 1, its topological structure is composed of low-voltage three single-phase bridges. A voltage drop and harmonic synchronous compensation method for a three-phase four-wire DVR system, comprising the following steps:

Step 1: Real-time sampling of the instantaneous values of the three-phase voltage and three-phase current of the grid. The detection method based on the improved instantaneous reactive power theory; PARK transformation is performed on the three-phase electricity in the abc coordinate system, and the three-phase electricity in the abc coordinate system is converted into the corresponding components in the dq coordinate system, namely:

Let the instantaneous value of the three-phase asymmetrical voltage be:

where the transformation matrix C is:

Step 2: Based on the dq transformation adopted in step 1, the voltage positive sequence fundamental wave components U _d0 and U _q0 are extracted by adding a low-pass filter.

Assuming that the fundamental effective value of phase A voltage in the three-phase system is U ₁ , the initial phase is The effective value of the nth harmonic is U _n , and the initial phase angle is Then there are:

Carry out coordinate transformation on the above formula, and then filter U _d and U _q components through a low-pass filter to obtain voltage positive sequence fundamental wave components U _d0 and U _q0 , where

Step 3. The voltage positive sequence fundamental wave components U _d0 and U _q0 extracted in step 2 are subjected to dq inverse transformation to obtain the voltage fundamental wave sine quantity, and the voltage drop amplitude and phase angle are calculated by using the method of constructing two-phase voltage with single-phase delay detection, get the effective value U ₁ ' of the drop voltage and the phase

By processing the DC component, the effective value and phase information of the drop voltage can be obtained as:

Step 4: Change the three-phase voltage αβ to obtain the variables u _α and u _β in the two-phase orthogonal coordinate system, perform αβ-dq transformation on u _α and u _β to obtain the d and q axis components U _d , U _q , combine Phase information provided in step 3 The d-axis fundamental wave component is obtained through a low-pass filter, and the inverse transformation result obtained through dq-αβ is the harmonic voltage fundamental wave quantity U _αf .

Referring to FIG. 2, it is a circuit diagram of a single-phase harmonic voltage detection applied in the present invention. Assume that the angular frequency of grid voltage is ω, and the initial phase angle of phase A voltage is The effective value of the grid voltage is E, then the instantaneous value of the voltage can be expressed as:

Transforming the instantaneous voltage into the αβ two-phase orthogonal coordinate system, the expression can be obtained:

where _C32 is the transformation matrix of the coordinate transformation.

where the transformation matrix C is:

Perform dq-αβ inverse transformation on the obtained d-axis fundamental wave component U' _d to obtain the harmonic voltage fundamental wave quantity:

U _αf ＝C ₃₂ ^-1 _U'd

Step 5. The fundamental wave value obtained in step 4 is subtracted from the system voltage by a subtracter to obtain a harmonic voltage value, which is used as a reference voltage input to the inverter. Taking phase A as an example, the fundamental wave quantity U _αf is subtracted from the voltage U _a of phase A of the system through a subtracter to obtain the corresponding harmonic voltage quantity U _ah .

Step 6. Use the reference voltage obtained in step 5 to construct the compensation voltage U _DVR from the drop voltage phase obtained in step 3, and perform equivalent reverse processing on the extracted harmonic voltage as the harmonic compensation voltage U _sh , see Fig. 3 is the harmonic voltage detection circuit diagram of the application of the present invention.

Step 7. Superimpose the drop compensation voltage U _DVR and the harmonic compensation voltage U _sh , generate compensation signals through the hybrid control method of feedforward control plus double closed-loop feedback control and PWM generator, and control the power switch of the inverter for compensation, see Fig. 4 is a schematic diagram of voltage drop and harmonic compensation applied in the present invention.

Example

In order to verify the effectiveness of the method of the present invention, the simulation software MATLAB/Simulink is utilized to simulate. The main parameters of the DVR simulation model in the simulation experiment are that the power supply is a 220V three-phase power supply, the capacity is 60kVA, and the switching frequency is 10kHz. The load is selected from a simple RL Resistive inductive load, where R=2.3Ω, L=0.5e-3H; use resistance voltage divider plus bypass switch switching method to simulate voltage drop, set the drop fault with harmonic grid voltage, and the sampling interval is 5e-5s, To verify the accuracy and rapidity of voltage drop detection and harmonic detection, the DVR system can simultaneously perform voltage compensation and harmonic compensation functions.

During the simulation, in order to verify the synchronous compensation effect of harmonics and voltage drops, the system voltage contains 3rd, 5th, and 7th harmonics in addition to the fundamental wave. In order to verify the accuracy of voltage drop detection and harmonic detection, set the Wave grid voltage drop fault; the simulation time is set to 0.5s, and the drop occurs between 0.1s-0.4s, accompanied by a 30° phase jump. The simulation is divided into two groups: single-phase drop and three-phase drop.

Figures 5-6 are single-phase voltage drop and harmonic compensation waveform diagrams and three-phase voltage drop and harmonic compensation waveform diagrams of the present invention, V _as is the system voltage waveform, V _d is the compensation voltage waveform obtained after the DVR detects the system voltage , V _aL is the load voltage waveform. It can be seen from the figure that the load voltage is hardly affected by harmonics and voltage drops.

From the above experimental simulation analysis, the method of the present invention can accurately collect harmonic signals on the basis of satisfying voltage drop compensation, which provides a good parameter basis for compensation; in the process of voltage drop and harmonic synchronous compensation, not only voltage drop can be realized Compensation, and at the same time, it has an obvious suppression effect on harmonics, which further improves the quality of the load voltage.

Claims (7)

1. the Voltage Drop and harmonic wave synchroballistic method of a kind of DVR system, which comprises the steps of:

Step 1 carries out PARK transformation to power grid three-phase voltage, obtains the component of voltage under dq coordinate system；

Step 2 carries out low-pass filter to amount after the component of voltage under dq coordinate system, extracts voltage positive sequence fundametal compoment；

Step 3, voltage positive sequence fundametal compoment carry out dq inverse transformation, obtain voltage fundamental sinusoidal quantity, are constructed using PHASE-LOCKED LOOP PLL TECHNIQUE Voltage Drop amplitude and phase；

Step 4 carries out α β variation to power grid three-phase voltage, obtains the component of voltage under α β coordinate system；

Step 5 converts to obtain d, q axis component to the component of voltage progress α β-dq under α β coordinate system, carries out dq- α after low-pass filtering β transformation, obtains harmonic voltage fundamental wave amount；

Step 6 makees fundamental wave amount and system voltage poor, harmonic voltage amount is obtained, as the reference voltage for inputting inverter；

Step 7 falls offset voltage and harmonic wave offset voltage according to reference voltage and drop-off voltage phase formation；

Step 8 will fall offset voltage and harmonic compensation voltage superposition, the mixing controlled by feedforward control plus Dual-loop feedback control Control method generates thermal compensation signal, and control inverter power switch compensates.

2. the Voltage Drop and harmonic wave synchroballistic method of DVR system according to claim 1, which is characterized in that step 1 The method for carrying out PARK transformation are as follows:

Wherein, U_d、U_qIndicate the component of voltage under dq coordinate system, U_a、U_b、U_cIndicate the three-phase voltage under abc coordinate system；

Transformation matrix C are as follows:

3. the Voltage Drop and harmonic wave synchroballistic method of DVR system according to claim 1, which is characterized in that step 2 Extract voltage positive sequence fundametal compoment method particularly includes:

If the fundamental wave virtual value of A phase voltage is U in three-phase system₁, initial phase isNth harmonic virtual value is U_n, initial phase angle isThe then three-phase voltage U under abc coordinate system_a、U_b、U_cIt indicates are as follows:

Low-pass filtered device is to U_dAnd U_qComponent, which is filtered, obtains DC component U_d0And U_q0, indicate are as follows:

4. the Voltage Drop and harmonic wave synchroballistic method of DVR system according to claim 1, which is characterized in that step 3 Obtained Voltage Drop amplitude and phase is expressed as:

In formula, U₁'、Indicate Voltage Drop amplitude and phase, U_d0、U_q0Indicate DC component.

5. the Voltage Drop and harmonic wave synchroballistic method of DVR system according to claim 1, which is characterized in that step 4 The method for carrying out α β variation are as follows:

If network voltage angular frequency is ω, A phase voltage initial phase angle isNetwork voltage virtual value is E, then three under abc coordinate system Phase voltage U_a、U_b、U_cIt indicates are as follows:

Instantaneous voltage is transformed in α β two-phase orthogonal coordinate system, then the component of voltage U under α β coordinate system_α、U_βIt indicates are as follows:

In formula, C₃₂For the transformation matrix of α β transformation.

6. the Voltage Drop and harmonic wave synchroballistic method of DVR system according to claim 1, which is characterized in that step 5 The method for determining harmonic voltage fundamental wave amount are as follows:

If the component of voltage U under α β coordinate system_α、U_β, carry out α β-dq and convert to obtain d, q axis component u '_d、u′_qIt respectively indicates are as follows:

Wherein transformation matrix C are as follows:

In formula, network voltage angular frequency is ω；

By acquired d axis fundametal compoment U '_dHarmonic voltage fundamental wave amount U can be obtained by carrying out dq- α β inverse transformation_αhIt indicates are as follows:

U_αf=C₃₂ ^-1U‘_d

In formula, C₃₂For the transformation matrix of α β transformation.

7. the Voltage Drop and harmonic wave synchroballistic method of DVR system according to claim 1, which is characterized in that step 7 Fall offset voltage using drop-off voltage phase and reference voltage construction, harmonic voltage is subjected to equivalent reverse process as harmonic wave Offset voltage.