1 APF active power filter device overview
With the increasing use of power electronic converters, electric energy has been more fully utilized. However, the wide application of nonlinear power device equipment produces a large number of distorted current harmonics. The flow of distorted current in the power grid leads to harmonic voltage; harmonic pollution increasingly threatens the safety, stability and economic operation of the power system. It has a significant impact on the linear load of the same network and other users. Harmonics have been combined with electromagnetic interference and power factor reduction as the three major public hazards of the power system. Therefore, understanding the principle of harmonic generation and studying the elimination of higher harmonics in power supply and distribution systems have a very positive significance for improving the quality of power supply and ensuring the safe and economic operation of power systems. Harmonic measurement is an important branch of the harmonic problem, and it has an important guiding role in suppressing harmonics and solving the problems caused by harmonics. Therefore, the measurement and analysis of harmonics is an important task in power system analysis and control, and it is an important prerequisite for relay protection and fault measurement.
The main harmonic generation sources are as follows:
1.1 Harmonic hazards
♦ Increase the additional loss of power components and cause fires.
Harmonics cause additional losses in components in the utility grid, reducing the efficiency of power generation, transmission, and electrical equipment. A large number of third harmonics flowing through the center line can overheat the line and even cause a fire.
♦ Affect the normal operation of electrical equipment.
Harmonics can affect the normal operation of electrical equipment, causing mechanical vibration and noise of the motor, causing severe overheating of the transformer, causing overheating of capacitors, cables and other equipment, insulation aging, and shortened service life, resulting in damage.
♦ Cause grid resonance.
This resonance may cause the harmonic current to be amplified several times or even tens of times, posing a great threat to the system, especially to capacitors and reactors connected in series, often causing capacitors and reactors to burn out.
♦ The relay protection is malfunctioned and the electrical measurement error is too large.
Harmonics will lead to relay protection, especially the microcomputer integrated protector and automatic device malfunction, resulting in unnecessary power interruption and production loss; harmonics will make the electrical measurement instrument measurement inaccurate, produce measurement error, give power management Economic losses caused by departments or power users.
♦ Crash the industrial control system.
The adjacent harmonic source or higher harmonics will cause interference to the communication and information processing equipment, and light noise will be generated, the communication quality will be lowered, the computer will not work normally, and the information will be lost and the industrial control system will collapse.
1.2 National standards based on harmonic control
GB/T14549-1993 "Power Quality: Harmonics in Utility Grid"
GB/T15543-2008 "Power Quality: Three-phase Voltage Allowable Unbalance"
GB/T12325-2008 "Power Quality: Supply Voltage Allowable Deviation"
GB/T12326-2008 "Power Quality: Voltage Fluctuation and Flicker"
GB/T18481-2001 "Power Quality: Temporary Overvoltage and Transient Overvoltage"
GB/T15945-2008 "Power Quality: Power System Frequency Allowance"
GB7625.1-1998 "Harmonic Current Limits from Low Voltage Electrical and Electronic Products"
GB/T15576-1995 "General technical conditions for low voltage reactive power static compensation device"
2 active power filter
2.1 Working principle
The ANAPF series of active power filter devices are connected to the grid in parallel. By detecting the harmonic and reactive components of the load in real time, PWM converter technology is used to generate a corresponding harmonic component and reactive component from the converter. The inverse component is injected into the power system in real time to achieve harmonic control and reactive power compensation.
2.2 Main technical features
DSP+FPGA full digital control mode with extremely fast response time;
Advanced main circuit topology and control algorithm with higher precision and more stable operation;
A multi-functional machine can not only compensate for harmonics, but also compensate for reactive power;
Modular design for easy production and commissioning;
Convenient parallel design for easy expansion;
It has perfect bridge arm over-current and protection function;
Easy to use, easy to operate and maintain.
2.3 Installation technical requirements
2.3.1 Arrangement requirements
ANAPF is generally a standard cabinet structure. It should be prevented from being inverted or laid flat during installation. The external dimensions are determined by the selected harmonic compensation current value. The layout of the plane is generally determined by the position of the harmonic current compensation point. The layout requirements are as follows
1) Installation from the wall: Under normal circumstances, it is recommended to arrange it with the low-voltage switchgear side by side, frontal operation, double-sided maintenance, and the rear maintenance passage is not less than 800mm.
2) Installation against the wall: ANAPF is also reliable wall layout, frontal operation, frontal maintenance.
3) When considering the system wiring and plane layout, the electrical designer should pay attention to the compensation access point of ANAPF as close as possible to the compensation object, and be in the upstream of the sampling CT, or reserve space at the end for design and installation. The downstream of the CT sampling cannot be included. Capacitive load. The layout is shown as follows:
4) All metal housings of ANAPF that are not energized under normal conditions shall be properly protected against zero or protective grounding according to the grounding standard (TN-S, TN-C-S, TT, etc.) required by the design.
2.3.2 Installation of transformers
1) The P1 end of the transformer points to the grid, and the P2 end points to the load.
2) Note that the input and output lines of the transformer should be consistent and in the right direction.
2.4 Main application areas and occasions
Airport: main control room, computer room, broadcasting system, EIB lighting dimming system, etc.
Hospital: ICU (intensive care unit), MRI (magnetic resonance imaging), operating room, medical imaging room, radiotherapy department, etc.
Theater, stadium: Resolve damage caused by harmonics of EIB dimming equipment and other control equipment.
School: Precision laboratory, computer room, network center, etc.
Research Institute: Precision instruments, computer rooms, and high-precision equipment concentration areas.
Large-scale shopping malls: Solving harmonic problems caused by the large number of applications of energy-saving lamps.
Bank: computer center, business department computer, security system, etc.
Taxation, industry and commerce: large computer center.
Telecom room: mobile base station.
Factory: PLC, computer control equipment, high-precision machine tools, PCS systems, metering/weighing systems, etc.
TV station: image equipment, dimming equipment, computers, etc.
3 Active Power Filter Function Module Introduction
3.1 Controller Module
APF active power filter device controller is mainly composed of: DSP (digital signal processor), FPGA logic device, AD signal sampling circuit, DI/DO input and output control circuit, PWM waveform control circuit, RS485 communication circuit, etc. Complete the collection and processing of voltage, current and other signals, the calculation of command current, the generation of switching circuits, the output of PWM signals, the external communication of the system and system protection. The control system is the core of the active filter, which determines the main performance and specifications of the active power filter system.
3.2 Converter Module
The core of the APF active power filter converter is the storage capacitor and IGBT module. The function of the converter is mainly to rectify the voltage of the grid through the IGBT power module to charge the storage capacitor, so that the bus voltage is maintained at a certain stable value. In this process, the converter mainly works in the rectification state, when the main circuit is generated. When the current is compensated, the converter operates in the inverter state. Considering that the product is running in the power grid for a long time, the DC support capacitor uses a film capacitor, and the power module uses German original products to ensure the quality of the whole machine. The choice of converter varies depending on the magnitude of the compensation current.
3.3 Reactor module
The APF reactor acts as a filter to filter out unwanted harmonics from the grid from the APF. Reactors can be divided into single-phase and three-phase, and currents range from 15A to 200A.
The core is made of high quality low loss silicon steel sheet;
The coil is wound with copper foil or aluminum foil;
Insulation adopts Class H, with longer service life and higher safety factor;
Wide power range: single unit from 15A to 100A.