The Application Of WIN-LV Inverter In High Power Motor In The Thermoelectricity Plant


The Application of WIN-LV Inverter in high power motor in the thermoelectricity plant

Prolegomena:

This essay represents Shenzhen Winner S&T Co., Ltd has successfully launched a series of low voltage high power inverters since 2006 based on its self-developed inverter parallel connection technology, positioning itself the first inverter manufacturer in China owning such technology.

Key word:

WIN-LV inverter, high power, inverter parallel connection technology

I Introduction of inverter connection in parallel technology

The so-called inverter parallel connection technology indicates that two or more sets of small power inverters are connected in parallel to drive a high power motor. However, since it is inverting frequency output, several problems as follows need be solved firstly:

1. When two or more sets of small power inverters are connected in parallel to drive a high power motor, it is required that their frequency, phase and limit must keep the same. Any hairlike bias will lead the system unstable, or trigger circumfluence among the inverting units.

2. The output must be the same, as accumulated bias in the frequency will cause regular fluctuate in the system’s output limit, and difference in phase will result in limit fluctuating.

3. High requirement to equalizing current. Equalizing current can be classified as active power equalizing current and reactive power equalizing current, namely the power equalization is classified as that of active power and reactive power.

4. On the aspect of protection, there must be a new function that can switch off the faulty inverter in time besides protection to the single inverter, which can guarantee the stability of the inverter.

Among the problems listed above, the most important is current equalization. So adopt the control mode of active power and reactive power parallel connection. Now, China’s current equalization technology is very mature, with unequalizing content within ±1% of the rated current. Shenzhen Winner has successfully launched low voltage high power inverters based on the parallel connection structure, and advanced SVPWM technology, photoelectrical isolation/transmission technology.

II Application

A large amount of pumps and fans in the power plants and the boiler industry have been reconstructed with the advanced frequency conversion speed control technology, with distinctive energy saving efficiency, majority of which, however, are low voltage motors with power lower than 315KW. Yet Shenzhen Winner has successfully reconstructed a high power AC motor (690V, 560KW) in a Fujian province-located thermoelectricity plant supported on its self-developed parallel connection technology.

Main advantages:

  • l No need to design the structure respectively
  • l Delivery period can be steeply shortened
  • l More easy to control the quality
  • l High performance but low cost

Prominent features of the parallel connection technology.

1. The common digital operator and control board can guarantee the balance of the system’s frequency, phase and limit

2. The common input and output compound reactor can ensure the balance of the output frequency.

3. The common DC bus realizes the parallel of active and reactive power, moving the current un-equalization problem.

4. All the parallel-connected inverter adopt digital control, making equalizing current control and communication more convenient, and realizing complex operation inside the module of the inverter, so as to enhance reliability of the system

1. ±20% voltage fluctuating width is quite applicable to Chinese grid status

2. The SVPWM technology, in addition to professional wave processing circuit, can reduce 1/3 heat loss and accordingly prolong the using life of the inverter.

3. The photoelectrical isolation technology is adopted in the inverter’s control circuit and drive circuit, to realize accurate signal receiving and control. Fault alarm and protection are pretty sensitive and accurate

4. various protection functions: over current, over load, over voltage, undervoltage, phase loss and shortcircuit

5. Flexible control mode: RS-485 control, PI regulating, multi-step speed, procedure control, proportion linkage, programming control terminals and analog signal terminal, several control mode

WINNER-branded inverter adopts the leading vector control technology, with main features as follows:

  • l Control mode: vector control, V/F control, vector control with PG, V/F control with PG.
  • l Owns motor parameter autotuning function, applicable for broad range of load.
  • l In the mode of open-loop, can realize rated torque output at low speed, speed control range hits 100:1
  • l In the mode of closed-loop, can realize full torque output at zero speed, with speed control range up to 1000:1
  • l Energy saving control function enables the inverter run with high efficiency. It can realize automatic operation with PID.
  • l Slip compensation function makes the system more stable
  • l Built-in automatic torque compensation realizes high starting torque.
  • l Torque control function enables the motor be able to run with a constant torque
  • l Friendly user interface, large screen LCD. Can realize parameter online monitoring and online regulation, in addition to parameter copy function, making operation more convenient.
  • l Less pollution to the grid

IV Comparison

1 air valve + motor: total investment cost: RMB 200,000

Equipment

Cost (RMB)

Motor (560kw)

100,000

Low voltage controller

100,000

Advantages: low investment cost, and simple system

Disadvantages: a) heavy starting current, low power saving efficiency
                             b) low control accuracy, and inconvenient maintenance

2 hydrodynamic coupling + motor:

total investment cost: RMB 260,000

Equipment

Cost (RMB)

Motor (560kw)

100,000

Low voltage controller

100,000

Hydrodynamic coupling

60,000

Advantages: small current, less impact on the grid, stable speed control,

Disadvantages: high investment cost, and high maintenance cost, and unsatisfying energy saving efficiency

3 inverter + motor: total investment cost: RMB 360,000

Equipment

Cost (RMB)

Motor (560kw)

100,000

Low voltage controller

100,000

Inverter

160,000

Advantages: prominent energy saving efficiency (30% or above), realize soft start and no impact on the grid, high reliability,

Disadvantages: harmonic current exists, bringing interference to the grid and peripheral devices

From the three tables above, it is easy for us to draw a conclusion that the third method can help the customer save 500KW×5000h×30%×0.4=336000 RMB more per year (providing the inverter works 5000 hrs per year). And it can realize economic benefits in half a year.

V Conclusion

Since Shenzhen Winner launched the year before the new models supported on the parallel connection technology, the company has received high appreciation and recognition with increasing orders.