STATCOM (Static Synchronous Compensator, also known as SVG). It is an important device for Flexible AC Transmission System (FACTS), which is the third generation of dynamic VAR compensation device after FC, MCR, and TCR type of SVC (Static VAR Compensator). Its appearance represents the application of most advanced technology for dynamic VAR compensation. It is also known as DSTATCOM when apply in power distribution. STATCOM is connected parallel in power grid and works as reactive current source. Its reactive current can be flexibly controlled and compensate reactive power for system automatically. It solves problem of harmonics interfere switching parallel capacitor banks. In another hand, it can restrain harmonics and improve power quality according to customers’ needs. STATCOM has superior performance in lots of aspect such as responding speed, stabilize voltage of power grid, reduce system power loss and harmonics, increase both transmission capacity and limit for transient voltage. It also has advantage of smaller in dimension.
STATCOM uses three phases powerful Voltage Sourced Converter as its core. Its voltage output connects system by through reactor or transformer. And regulates AC voltage amplitude and phase of inverter to absorb or produce reactive power for system. As sourced compensation device, STATCOM not only monitoring and compensates current for impact load but also compensate and monitoring harmonic current.
Depending on advantages of powerful technology and human resource, Beijing PONOVO introduces several types of STATCOM with different topology to meet customers’ various needs. AccuVar ASVC – 100 type of DSTATCOM applies chained-multilevel structure and featured with compact design, less power loss, fast respond and module configuration for easier expansion and maintenance. Major control system adopts DSP and FPGA with layered structure which enables high-speed adaptive computation, multi-chained expansion and flexible configuration for system.
It has been applied in industry of coal mine, wind power system, metallurgy, electrified railway and power distribution for urban and rural area (suitable for power distribution system with 3kv to 35kv).
AccuVar ASVC has superior advantages compare with conventional fixed capacitor compensator, MCR and TCR.
1. Fast reactive power adjustment
AccuVar ASVC provides continuous dynamic compensation to power factor along the load variation. It completely eradicates capacitive reactive power delivery to the power grid and maintain power factor in designed value for power grid. AccuVar ASVC has advantages:
- Fast response, able to implement dynamic compensation in real time.
- Effectively avoid parallel resonance.
- Able to produce and absorb reactive power.
- Deliver less harmonic to system.
2. Restrain voltage fluctuation and flicker
Power grid voltage has fluctuation and flicker when high power impact load is operating. Voltage fluctuation and flicker bring negative influence to other nearby customers’ electricity usage and sensitive load by decreasing safety for electricity usage and decreasing efficiency for production, increasing risk of faulty production. AccuVar ASVC’s response time is less than 1ms and it provides smooth dynamic compensation for reactive power. It is more efficient to restrain voltage flicker and reduce voltage fluctuation, improve voltage to meet standard.
3. Constant current, effectively restrain voltage drop
AccuVar ASVC has characteristic of constant current. It has advantage in voltage control due to its reactive current output is not affected by busbar voltage. System needs more dynamic reactive power when system voltage gets lower. AccuVar ASVC’s reactive current output is not related to system voltage, but the conventional capacitor VAR compensator’s reactive power output is proportional to square value of voltage. AccuVar ASVC can provide better support for improving low voltage ride through (LVRT) characteristic in wind power.
4. Compensate negative sequence, implement balanced power supply
AccuVar ASVC has unique chained structure to allow split-phase adjustment and realizes energy interchange between different phases. It provides balanced compensation to load negative sequence by applying Steinmetz balanced principle. AccuVar ASVC makes current flow into system with balanced power and desired reactive power.
5. Resistance to harmonics, able to compensate the part of harmonic current
Due to widely applications of nonlinear load, harmonics threat public power grid worse than before. Harmonics cause equipment overheat, insulation depletion, extra power loss, decrease efficiency of power system and electrical equipment. It also cause malfunction of protection relay and malfunction of automatic device, inaccuracy of measurement and interfere nearby communication system. It is possible to have fire hazard when 3rd harmonic flow through natural line and makes line overheat. AccuVar ASVC applies carrier phase shift multi-level PWMï¼ˆPulse Width Modulationï¼‰control strategy and its high frequency equivalent switch can filtering partial load harmonics without amplifying them and no harmonic resonance. It makes possible for multi-function in on equipment.
- Provides fast smooth dynamic compensation from inductive to capacitive in reactive power. Also eradicates reactive power delivery to the power grid. It meets the maximum request to compensate power factor, keeps power factor close to 1.0 at anytime.
- Low power loss, better economical operation.
- Has powerful ability to support voltage and ability to withstand short-time overload. Provide better support for improving low voltage ride through (LVRT) characteristic for wind turbine. Decrease negative influence which caused by repetitive switching operation to the wind turbine.
- Faster response time and better effect for restraining flicker.
- Produce no harmonic and filtering partial load harmonic without amplifying harmonic and no harmonic resonance. It has better safety and stability due to it is not sensitive to the system parameters.
- Modules designed, easy for installation and maintenance. Redundant N+1 structure provides high reliability.
- Less space for installation, also provides flexible installation, equipment can be installed indoor/outdoor.
- Low loss and low noise.
- AccuVar ASVC circuit applies high power switch controlled electrical and electronics components to construct phase-change bridge circuit. The circuit connects through inductor in parallel with grid. To implement reactive compensation by adjusting amplitude and phase of AC voltage or directly adjust AC current in bridge circuit to make circuit absorb or produce reactive current.
- AccuVar ASVC has real power/ reactive power exchange with system. This is implemented by control the amplitude and phase angle of chained converter voltage output.
- AccuVar ASVC circuit connection shows below, phase converter is structured by chain knots
- Converter’s IGBT valve adopts optimize carrier phase-shift modulation. Multiple knots equivalent switch has high frequency and has extremely low harmonic output. Voltage output wave form shows below