Mitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
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Compact Variable Speed Drive System
for Compressor Driver with Low CAPEXand Low OPEX which born under New Idea

M i ts u b i s h i H e a v y I n d u s t r i e sCompressor Corporation

In recent years, there have been moves toward motorization in many fields to facilitate
operation and reduce maintenance costs. In the industrial equipment field, the number of cases
where electric motors are adopted for drivers has increased.
Motors have conventionally been operated at a constant frequency of 50Hz or 60Hz. Alongwith the increase in the capacity of frequency converters (inverters), motors have been used aslarge-capacity and variable-speed drivers with the frequency being changed.
With such a background, the number of electric variable speed drivers used in large-capacity
compressors has been increasing.
On the other hand, the number of large-capacity electric variable speed drivers used is yet
few, and the number of manufacturers of transformers and inverters requiring such a special
capacity are limited. Therefore, the customer's equipment purchase cost increases, and theoperating cost also increases due to the power loss of the transformer and inverter. These
increased costs are the negative factors in introducing them.
In order to solve the aforementioned issues, a new idea was produced where the main powerof a compressor is supplied by a large capacity constant speed motor and the power contributing to
the variable speed is supplied by a small-capacity variable speed driver. Under this new idea, a
low-cost and high-efficiency variable speed driver for compressor drivers, the IMG-VSDS(Integrated Motor Gear - Variable Speed Drive System), was developed, in which two powers areintegrated at the speed-increasing gear. A 6MW prototype device was manufactured, and various
tests such as overload and severe tests were conducted and the IMG-VSDS was produced.
This report introduces the IMG-VSDS product.

|1. Features of IMG-VSDS
1.1

Configuration of train using IMG-VSDS

The IMG-VSDS, an electric variable speed driver, was produced for the purpose of reducing
cost and increasing efficiency. Electricity is used because it is easy to handle and acts as a driving
source in the driver.

Figure 1

Configuration of compressor train using IMG-VSDS

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
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Figure 1 shows the train configuration with a compressor as the driven equipment. In thissystem, a constant-speed, conventional motor with 4 poles is used for the main driver, and anelectric variable speed driver (IMG-VSDS), which is composed of a small-capacity variable speed
motor and a speed-increasing gear (differential planetary speed-increasing gear), is provided
between the constant speed motor and the compressor. This system can be operated in a wide
operating range for the compressor and achieves cost reduction, increased efficiency and highreliability.

1.2

Variable speed configuration

Figure 2 illustrates the configuration in which the speed of the driven equipment is madevariable by the IMG-VSDS. In this configuration, the ring gear which is connected to the main
driver and rotates at a constant speed and the planetary carrier which is connected to thesmall-capacity variable speed motor and rotates at variable speed are combined, so that the sun gear
connecting to the driven equipment operates at variable speed. This configuration can reduce thepower of the IMG-VSDS variable speed motor at the rated speed of the compressor to about 1/10of the total power of the train.

Figure 2

Configuration for variable speed with IMG-VSDS|2. Comparison with conventional variable speed motor driver
The power of the variable speed motor in the IMG-VSDS is about 1/10 of all power. The
power flow in the IMG-VSDS and that in a conventional variable speed motor are depicted in
Figure 3. The variable speed motor requires the addition of a transformer and an inverter because of
its characteristics. The loss caused by these devices is proportional to the power and when thepower is reduced to 1/10, the loss is reduced to 1/10. As can be seen in Figure 3, in the train of
IMG-VSDS, the power of the transformer and the inverter is reduced and the loss is minimized,
resulting in increased efficiency in the entire train.
Figure 4 gives a comparison of the efficiency between the IMG-VSDS train and aconventional variable speed motor train. Due to the aforementioned factors, the efficiency of theIMG-VSDS is substantially increased compared with that of the conventional variable speed motor.
In addition, the cost for the transformer and inverter in a variable speed motor largely affects
the overall price. Therefore, the reduction of the required power in the IMG-VSDS suppresses theprice of the entire train compared with a conventional variable speed motor train. At the same time,the electric room where the transformer and inverter are placed was made compact and the amountof air conditioning equipment and related costs were also reduced.

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
3Figure 3

Power flow of IMG-VSDS and conventional variable speed motor

Figure 4 Comparison of efficiency between IMG-VSDS train and conventional variable speedmotor train|3. Specifications for commercialization
The IMG-VSDS has three models in the series which correspond to the respective powers of4MW, 6.3MW and 10MW of compressors as the driven equipment, with the variable speed of thecompressor ranging from 75% to 105%. The standard specifications are presented in Table 1. If therated speed of the compressor differs from those in Table 1, customer requirements can be met bypartially changing IMG-VSDS speed-increasing gear parts.
Table 1 Standard specifications of IMG-VSDS
ModelCompressor power (MW)Compressor rated speed (rpm)

IMG04

IMG06

IMG1046.3

1011200

10000

12500

Variable speed range (%)

75-105

Power supply frequency (Hz)50 / 60

Main driver speed (rpm)(4P constant speed motor)

1500 / 1800

Figure 5 shows an overview of the compressor train using the IMG-VSDS. The compressor,
the IMG-VSDS and the main driver are placed on the common baseplate to make the compressor
train compact. A arrangement where a lubricating oil system is integrated in the configuration as
illustrated in Figure 5 to make it more compact is also available.

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
4Figure 5

Overview of compressor train using IMG-VSDS|4. Future development
The trend toward electrification has been continuing and the market demand for lower prices
and higher efficiency have been increasing. In order to meet this demand, we put the electricvariable speed driver developed under the new idea into commercial production.
By supplying the high-efficiency and low-priced, compact electric variable speed driver
simultaneously with our high-efficiency compressor, we can minimize customer capital
expenditure and operating costs for the future. In addition, now that the variable speed driver has
been produced, we can quickly respond to customer issues on the entire compressor train.
Moving forward, we will make efforts to respond to diversifying customer demands andpromote technical innovation and the development of new products from the customer’s
perspective.