PQSVG
STATIC VAR GENERATOR FOR LOW VOLTAGE
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PQSVG static var generator is a new active dynamic reactive power and harmonic compensation device with high cost performance. This device can do real-time tracking compensation to harmonic, reactive power which changes in both size and frequency and three phase unbalance, thus can provide fast dynamic reactive power compensation and harmonic filtering for power grid and electrical loads. It can effectively improve transit stability of power grid voltage, suppress bus bar voltage flicker, compensate unbalanced loads, filter the harmonic and improve the power factor.

PQSVG can be widely used in oil and chemistry, metallurgy, electricity, coal, electric railway, wind power plant that have impact loads and large-capacity motors.

Working Principle

SVG - Static Var Generator, (named SVG for short, also named STATCOM), is the representative of the latest technology in the reactive power compensation now, belongs to the important parts of flexible AC transmission system (FACTS). SVG is in parallel in the grid, which is equal to a controllable reactive current source, its reactive current changes along with the change of load reactive current, automatically compensate reactive power required by grid system and harmonic filtration, and realize dynamic step-less compensation to grid reactive power and harmonic.

PQSVG uses gate-controlled power electronic device (such as IGBT) to constitute self-commutation bridge type circuit, in parallel with grid by reactor, suitably adjust output voltage amplitude and phase at the AC side of bridge type circuit, or directly control its AC side current, then can make this circuit to absorb or generate required reactive current, to achieve the purpose of dynamic reactive power compensation.

PQSVG working principle (direct control type)

As shown in picture, SVG is constituted by instruction current arithmetic circuit and compensation current generating circuit. Instruction current arithmetic circuit real-time monitor load current, converse analog current signal into digital signal, send it to digital signal processor (DSP) to process signal, extract the reactive current and harmonic current of fundamental wave to get the directive current, and follow the control and drive circuit through current, send out drive pulse to compensation current generating circuit in the form of pulse width  modulation (PWM), to drive IGBT or IPM power module, generate reverse and equivalent compensation current to inject into grid, thus can realize dynamic, fast, thoroughly manage the load reactive current and harmonic current.

Device Structure

Device structure diagram

Main Functions

(1) Maintain receiving end voltage, strengthen system voltage stability
For the load center, dut to large capacity and no large reactive power as support, it is easy to cause grid voltage on the low side and voltage collapse accident. While SVG has fast reactive power adjustment ability, it can maintain load side voltage, to improve voltage stability of power supply system at load side.
(2) Compensate system reactive power, improve power factor, reduce line loss, save energy and reduce cost
A variety of loads in electricity system such as asynchronous motors、electric arc furnace, rolling mill and large capacity rectifying equipment and so on will need a large number of reactive power during working; at the same time, transformer and line impedance in the power distribution grid will also generate some reactive power, that will reduce the system power factor.
For electric power system, load’s low power factor will increase energy loss and voltage drop of power supply line, which reduced voltage quality. Meanwhile, reactive power also cause the reduction of availability of power generation, power distribution, power supply equipment; for electric consumer, low power factor will increase electricity bill, increase production cost.
(3) Suppress voltage fluctuation and flicker
The voltage fluctuation and flicker are mainly caused by load dramatic change. This change will cause current sharp fluctuation, cause the electric power grid voltage flicker. The typical loads that cause voltage flicker have electric arc furnace, rolling mill, electric locomotive and so on.
SVG can fast provide varying reactive current, to compensate voltage fluctuation and flicker caused by load changes.
At present, the best equipment to suppress voltage fluctuation and flicker is SVG.
(4) Filter the harmonics
There are a large number of non-linear loads in power distribution grid such as inverter, internal mixer, elevator and arc furnace. They cause grid has a lot of harmonic, voltage/current waveform distortion, electrical equipment fault rate increase, distribution system loss increase, and even happen grid resonance which lead to trip accident. PQSVG can generate equivalent and reverse compensation current to filter harmonic, the maximum compensation capacity is 30% of device capacity.
(5) Suppress three phase unbalance
Power distribution grid has many three phase unbalanced loads, such as electric locomotive traction loads and AC furnace. The three phase impedance unbalance of line, transformer and other distribution equipment will also cause voltage unbalance.
PQSVG can fast compensate negative current generated by unbalanced loads, always insure the three phase current to grid is balanced, greatly improve the quality of power supply.

Technical Advantages

SVG is the most advanced reactive power device at now. The compensation device based on voltage source type inverter has realized a qualitative leap of reactive power compensation mode. It not longer use capacitance and inductance devices of large capacity, but through high-frequency switch of high-power electronic device to realized conversion of reactive energy. Technically speaking, PQSVG has the following advantages compared traditional reactive power compensation device:

(1) Faster response speed
SVG response time ≤ 10 ms. while traditional SVC response time ≥ 20 ms (if too fast, may cause oscillation of  reactor and capacitor).
SVG can complete interconversion from rated capacitive reactive power to rated inductive power within a very short time, this incomparable response speed completely can be competent to the impact load compensation.
(2) Stronger voltage flicker suppress ability
The suppress of SVC on voltage flicker can be 2:1 at most, while SVG can be 5:1 or even higher. Being subject to the limitation of response speed, SVC’s voltage flicker ability will not increase along with the increase of compensate capacity. But as SVG has faster response speed, increasing device capacity can continuously improve its voltage flicker suppress ability.
(3) Wider operating range
The output current of SVG is not depend on the voltage, performed as the characteristics of constant current source, can work among the ranges of rated inductive to rated capacitive, has wider operating range. While the nature of SVC is impedance compensation, the output current and voltage have linear relation. So when system voltage reduces, SVG can proved greater compensation capacity compared with the same capacity SVC, the characteristic of voltage and current are as follows,
SVG/STATCOM                                            SVC

(4) Diversified compensation function
PQSVG not only has fast reactive power compensation functions, but also can compensate load harmonic current, negative-sequence current and other power quality problems based on user actual requirement.
(5) Low switch ripple output characteristic
PQSVG use two same three phase full bridge inverters in parallel, which improved equipment capacity; and IGBT drive used PWM switch ripply cancellation technology which has our own patent, greatly reduced output ripple wave, circuit diagram as follows picture
SVG inverter principle diagram

SVG inverter PWM switch stagger ripple wave cancellation technology

As shown in picture, the output current through PWM switch stagger technology, the ripple wave of output current ia composite by  ia1 and ia2 greatly reduced, the surplus ripply current was filtered by switch ripply wave filter.

Performance Features

Higher efficiency, lower loss
  • Patented technology of ripple cancellation and stagger converter is characterized by high current tracing speed, small ripple and low loss.
  • Multi-DSP collaborative control can guarantee highly accurate control and high-speed computation.
More functions, more modes
  • Reactive power and harmonic integrated compensation, meet compensation requirement of series kind of power distribution system.
  • Settable harmonic gradation compensation function.
  • Balance compensation function, can balance load current among each phases.
  • RS-485, RS-232, TCP/IP port, standard MODBUS RTU communication protocol, and computer remote monitoring function.
More stable, more reliable
  • Optical fiber drive can guarantee high security, reliability and anti-jamming capability.
  • Multi-protection, strict thermal design can ensure the secure and reliable operation of the system.
  • Advanced control algorithms, Adapt to all kinds of complicated field and stable operation.
  • Digital control, LCD working platform English.
  • Self-diagnosis function.
  • Record of historical events function.
Higher power density, easier installation and maintenance
  • Modular design of controller and power module can guarantee high power density, and easy installation and maintenance.
  • It can conduct multi-machine parallel operation to satisfy various needs for compensation capacity.
  • Automatic current limiting will be conducted once output capacity is fully loaded,  so it is free of the trouble in overloading.
  • Detection methods of source current and load current are optional for the convenience of field installation.
PQSVG link
  • PQSVG technical parameter
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