CN104362655A - Unbalanced load compensation device and compensation method - Google Patents

Abstract

The invention relates to a compensation device and a compensation method applied in microgrids and low-voltage power distribution grids, and in particular relates to an unbalanced load compensation device and an unbalanced load compensation method. The compensation method utilizing the compensation device comprises the following steps: carrying out real-time acquisition on the voltages and the currents of a power grid via digital signals; carrying out necessary filtering processing on power grid voltage and current signals acquired in real time, then sending the current signals acquired in real time into a three-two coordinate transformation system, transforming the current signals into a dq0 coordinate system and performing compensation calculation on the currents; returning a duty ratio obtained in a calculation manner into an abc coordinate system so as to perform real-time compensation, and carrying out single processing on a fourth bridge arm specially used for a zero line current, thereby realizing the purpose of real-time compensation of unbalanced loads. According to the method, the voltages and currents of the power grid and the real-time currents of an IGBT (Insulated Gate Bipolar Transistor) can be monitored and protected while the compensation of unbalanced loads is finished at the same time, and the signals acquired in real time are stored and processed.

Description

An unbalanced load compensation device and compensation method

technical field

The invention relates to a compensation device and method in an electric low-voltage distribution network, in particular to an unbalanced load compensation device and a compensation method.

Background technique

In the existing traditional three-phase four-wire distribution transformer wiring system in my country, due to various reasons such as the low-voltage single-phase load cannot be fully divided manually, the actual operating rate of the distributed load is different, and the three-phase load is unbalanced. It is inevitable. And this unbalanced three-phase load will inevitably lead to increased loss, decreased power efficiency, increased zero-sequence current, and shortened service life of equipment.

Harm to the transformer: The unbalanced three-phase load will make the transformer run asymmetrically, which will increase the loss of the transformer. According to the transformer operating regulations, the neutral current of the transformer in operation cannot exceed 25% of the rated current of the low-voltage side of the transformer. In addition, the unbalanced three-phase load will cause excessive zero-sequence current of the transformer, increase the temperature of some metal parts, and even cause the transformer to burn out. Neutral line and neutral point voltage problems: The zero-sequence current of the neutral line is too large, causing the neutral line to burn out, causing problems such as excessive neutral point voltage offset. Harm to electrical equipment: The unbalanced three-phase load will increase the reverse torque in the motor, which will cause the motor to heat up, the efficiency will decrease, and the energy consumption will increase. Therefore, the unbalanced three-phase load will shorten the service life of electrical equipment, accelerate the replacement frequency of equipment components, and increase equipment maintenance costs. At present, the phase-separated reactive power compensation device with the best compensation effect on the market can compensate the load, but it can only compensate for the reactive current part in the system, but it is powerless for the asymmetrical active current part. The current imbalance may be even greater, so the power supply department of the electric industry can only adjust the load by manual branching.

It can be seen from the above that the unbalanced three-phase load of the power consumption system has very serious harm and influence on transformers, electrical equipment and power consumption systems, and especially constitutes a great obstacle to the full and effective use of electric energy. In today's shortage of power supply, it is an urgent task to solve the three-phase unbalance problem of the power system.

Contents of the invention

In order to solve the problem that the three-phase load imbalance of the power grid cannot be effectively resolved, the invention provides an unbalanced load compensation device and a compensation method.

The present invention is realized by adopting the following technical scheme: an unbalanced load compensation device, including a three-phase four-arm full-bridge inverter circuit with two IGBTs connected in series, a Hall voltage sensor, and a Hall current sensor. , A digital signal processor DSP and a PWM drive module with a phase-locked loop program written in it, the digital signal processor DSP includes a proportional integral controller, and the input end of the three-phase four-arm full-bridge inverter circuit passes through the inductor and the three-phase Four-wire grid connection, the output end of the three-phase four-leg full-bridge inverter circuit is connected to the DC side capacitor and connected to the DC voltage input end of the digital signal processor DSP, the primary side of the Hall voltage sensor and the Hall current sensor are both It is connected to the three-phase four-wire grid, the secondary side of the Hall voltage sensor and Hall current sensor is connected to the input end of the filter circuit, the output end of the filter circuit is connected to the input end of the digital signal processor DSP, and the digital signal processor DSP The output terminal is connected to the output terminal of the PWM driving module, and the output terminal of the PWM driving module is connected to the control terminal of the IGBT.

Utilize the compensation method of above-mentioned compensating device, comprise the following steps:

S1: The Hall voltage sensor and the Hall current sensor sample the phase voltage, phase current and neutral current of the three-phase four-wire grid in real time, and input the sampled phase voltage, phase current and neutral current to the filter circuit for filtering processing;

S2: The filtered phase voltage, phase current and neutral current are input into the digital signal processor DSP, and the phase-locked loop program in the digital signal processor DSP generates a reference phase according to the phase voltage;

S3: The filtered phase current passes through the 3/2 coordinate transformation system in the digital signal processor DSP and converts it into the current Id and Iq in the d, q rotating coordinate system according to the reference phase, and the neutral current is obtained after sampling the current In;

S4: The digital signal processor DSP subtracts the preset DC voltage reference value from the actual DC voltage value input by the three-phase four-arm full-bridge inverter circuit to obtain the DC voltage difference ΔU, and the DC voltage difference ΔU is proportionally integrated The controller obtains the d-axis current target reference value;

S5: Subtract the obtained current Id from the d-axis target reference value to obtain the amount to be compensated on the d-axis, subtract the current Iq from the q-axis target reference value to obtain the amount to be compensated on the q-axis, and subtract the current In from the 0-axis target reference value Get the amount to be compensated on the 0-axis, and set the q-axis target reference value and the 0-axis target reference value to zero;

S6: Send the amount to be compensated to the proportional-integral controller, and the proportional-integral controller obtains the duty cycle values Dd, Dq and D0 of the d-axis, q-axis and 0-axis;

S7: Send the above-mentioned duty cycle values Dd and Dq into the 2/3 conversion coordinate system to obtain the respective duty cycles Da, Db, Dc in the three-phase coordinate system and send the sum D0 to the corresponding IGBTs to control the IGBTs to turn on and shutdown;

S8: The DC side voltage of the three-phase four-leg full-bridge inverter circuit is maintained constant by the duty cycle Da, Db, Dc and D0, and the AC side of the three-phase four-leg full-bridge inverter circuit is compensated by the output compensation current to the three-phase In the four-wire grid, the load of the three-phase four-wire grid is balanced.

The traditional compensation method focuses on the harmonic processing of the power grid, but this device can output compensation current to the power grid to balance the load of the power grid, and the adjustable unbalance range of the device is large. The compensation method of this device is simple and does not need to calculate q Axis and 0-axis target reference values, so the calculation speed is fast, the hardware requirements of the device are low, the dynamic compensation effect is good, and continuous dynamic compensation under large unbalanced load conditions can be realized.

Description of drawings

Figure 1 is a schematic structural diagram of the compensation device.

Fig. 2 is a flowchart of the compensation method.

Figure 3 is a current waveform diagram when the grid load is unbalanced.

Fig. 4 is a waveform diagram of the grid current after compensation by the compensation device.

Fig. 5 is a control algorithm diagram of the compensation device.

Detailed ways

An unbalanced load compensation device, including a three-phase four-arm full-bridge inverter circuit composed of two series-connected IGBTs, a Hall voltage sensor, a Hall current sensor, and a digital phase-locked loop program written in it. The signal processor DSP and PWM drive module, the digital signal processor DSP includes a proportional integral controller, the input end of the three-phase four-bridge arm full-bridge inverter circuit is connected to the three-phase four-wire grid through an inductor, and the three-phase four-arm full-bridge inverter circuit is connected to the three-phase four-wire grid. The output terminal of the bridge inverter circuit is connected to the DC side capacitor and connected to the DC voltage input terminal of the digital signal processor DSP. The primary sides of the Hall voltage sensor and the Hall current sensor are connected to the three-phase four-wire grid. The Hall voltage The secondary side of the sensor and the Hall current sensor is connected to the input end of the filter circuit, the output end of the filter circuit is connected to the input end of the digital signal processor DSP, the output end of the digital signal processor DSP is connected to the output end of the PWM drive module, The output terminal of the PWM driving module is connected to the control terminal of the IGBT.

Utilize the compensation method of above-mentioned compensating device, comprise the following steps:

S1: The Hall voltage sensor and the Hall current sensor sample the phase voltage, phase current and neutral current of the three-phase four-wire grid in real time, and input the sampled phase voltage, phase current and neutral current to the filter circuit for filtering processing;

S2: The filtered phase voltage, phase current and neutral current are input into the digital signal processor DSP, and the phase-locked loop program in the digital signal processor DSP generates a reference phase according to the phase voltage;

S3: The filtered phase current passes through the 3/2 coordinate transformation system in the digital signal processor DSP and is transformed into the current Id and Iq in the dq rotating coordinate system according to the reference phase, and the neutral line current is obtained after sampling the current In;

S4: The digital signal processor DSP subtracts the preset DC voltage reference value from the actual DC voltage value input by the three-phase four-arm full-bridge inverter circuit to obtain the DC voltage difference ΔU, and the DC voltage difference ΔU is proportionally integrated The controller obtains the d-axis current target reference value;

S5: Subtract the obtained current Id from the d-axis target reference value to obtain the amount to be compensated on the d-axis, subtract the current Iq from the q-axis target reference value to obtain the amount to be compensated on the q-axis, and subtract the current In from the 0-axis target reference value Get the amount to be compensated on the 0-axis, and set the q-axis target reference value and the 0-axis target reference value to zero;

S6: Send the amount to be compensated to the proportional-integral controller, and the proportional-integral controller obtains the duty cycle values Dd, Dq and D0 of the d-axis, q-axis and 0-axis;

S7: Send the above-mentioned duty cycle values Dd and Dq into the 2/3 conversion coordinate system to obtain the respective duty cycles Da, Db, Dc in the three-phase coordinate system and send the sum D0 to the corresponding IGBTs to control the IGBTs to turn on and shutdown;

S8: The DC side voltage of the three-phase four-leg full-bridge inverter circuit is maintained constant by the duty cycle Da, Db, Dc and D0, and the AC side of the three-phase four-leg full-bridge inverter circuit is compensated by the output compensation current to the three-phase In the four-wire grid, the load of the three-phase four-wire grid is balanced.

During specific implementation, the digital signal processor DSP is equipped with a communication module, through which the external monitoring system can communicate, and the signals such as voltage and current can be observed through the monitoring system.

Claims (2)

1. a unbalanced load compensation arrangement, it is characterized in that comprising the three-phase four-arm full bridge inverter that brachium pontis is made up of the IGBT of two series connection, Hall voltage transducer, Hall current sensor, with the digital signal processor DSP of phase-locked loop program and PWM driver module in it, pi controller is comprised in digital signal processor DSP, the input of three-phase four-arm full bridge inverter is connected with three-phase and four-line electrical network by inductance, the output of three-phase four-arm full bridge inverter is connected with DC bus capacitor and is connected with the DC voltage input end of digital signal processor DSP, Hall voltage transducer is all connected with three-phase and four-line electrical network with the former limit of Hall current sensor, Hall voltage transducer is connected with the input of filter circuit with the secondary of Hall current sensor, the output of filter circuit is connected with the input of digital signal processor DSP, the output of digital signal processor DSP is connected with the output of PWM driver module, the output of PWM driver module is connected with the control end of IGBT.

2. utilize a compensation method for the compensation arrangement described in claim 1, it is characterized in that comprising the following steps:

S1: the phase voltage of Hall voltage transducer and Hall current sensor real-time sampling three-phase and four-line electrical network, phase current and current in middle wire, and the phase voltage of sampling, phase current and current in middle wire are input to filter circuit carry out filtering process;

S2: in filtered phase voltage, phase current and current in middle wire supplied with digital signal processor DSP, the phase-locked loop program in digital signal processor DSP produces fixed phase according to phase voltage;

S3: filtered phase current is converted into electric current I d, Iq under d, q rotating coordinate system in digital signal processor DSP through 3/2 coordinate transform system and according to fixed phase, current in middle wire obtains electric current I n after over-sampling;

S4: digital signal processor DSP is by the direct voltage reference value preset and input actual DC magnitude of voltage by three-phase four-arm full bridge inverter and subtract each other and obtain direct voltage difference Δ U, and direct voltage difference Δ U obtains d shaft current target reference through pi controller;

S5: the electric current I d of gained and d axle target reference subtract each other and obtain d axle amount to be compensated, electric current I q and q axle target reference subtract each other and obtain q axle amount to be compensated, electric current I n and 0 axle target reference subtract each other and obtain 0 axle amount to be compensated, and q axle target reference and 0 axle target reference are all set to zero;

S6: amount to be compensated is sent in pi controller respectively, pi controller obtains dutyfactor value Dd, Dq and D0 of d axle, q axle and 0 axle;

S7: above-mentioned dutyfactor value Dd, Dq are sent into 2/3 converted coordinate system obtain three phase coordinate systems under respective duty ratio Da, Db, Dc sum D0 is delivered to each self-corresponding IGBT, control IGBT turns on and off;

S8: the DC voltage of three-phase four-arm full bridge inverter remains constant by duty ratio Da, Db, Dc and D0, three-phase four-arm full bridge inverter AC then exports offset current and compensates in three-phase and four-line electrical network, makes the load balancing of three-phase and four-line electrical network.