AC7 matrix converter

AC7 matrix converter

AC7 Matrix Converter

The combination of an adjustable frequency drive (AFD) and motor

has enjoyed widespread use because of its excellent energy-saving

capabilities Despite these advancements, there are still issues to be

conquered such as the suppression of input power harmonics and

the effective use of electric energy regenerated during deceleration.

In order to fully solve these technical issues, Yaskawa is the first in

the world to commercialize the AC7 Matrix Converter: a new

technology that converts the AC power source directly into a variable

AC output.

This paper shows the data and outlines the AC7 Matrix Converter

principle, PWM method, and input current control It also explains the

specifications and features of the AC7 Matrix Converter.

1 Introduction

With the depletion of energy resources and the increase in

energy consumption, energy conservation is becoming a high

priority in many sectors Energy conservation has become a

key issue in the field of motor drives, and the use of PWM

drives is increasing as one effective means of reducing

energy consumption Major applications include industrial

uses such as converting, transport, and fabrication, as well

as commercial applications such as fans and pumps for

indoor comfort

In recent years, the growing use of PWM drives has led to

increased focus on the various problems inherent in drives,

such as insulation failure due to surge voltage at the motor

terminals, bearing fluting electro-corrosion due to shaft

potential, and other output-side problems Other difficulties

include input-side issues such as the effects on power supply

equipment and other systems connected in parallel running

off the same power supply

To resolve these problems, Yaskawa has commercialized

drives such as the G7 with 3-level PWM control technology to

control surge voltage and leakage current and the DC5

sine-wave PWM converter permitting input power supply

regeneration and control of input power supply harmonics

The latest technology in this area is the AC7 Matrix

Converter, the first of its type in the world, offering

improvements in motor drive environmental characteristics

including motor surge voltage, power supply harmonics, and

shaft potential

2 Basic Principles of the Matrix Converter

Unlike conventional voltage-type PWM drives, the AC7 uses

matrix conversion technology for direct conversion of AC to

AC [1] Features such as power supply regeneration and

suppression of power supply harmonics make it an ideal

choice as a drive for applications where regenerative

operation is highly beneficial, such as elevators, escalators,

centrifuges, and test stands

The main circuit for a matrix converter consists of a compact

input filter and nine bidirectional switches (Figure 1) The

bi-directional switches are made up of IGBTs and diodes The

basic characteristics of this type of matrix converter are

discussed below

Figure 1: Diagram of Main AC7 Matrix Converter Circuit

2.1 PWM method

The AC7 uses PWM switching to output power from the three-phase AC power supply at a specified voltage and frequency Figure 2 below shows an example of a PWM-switched waveform In Region 1, switching of the R phase (maximum voltage) is handled referenced to phase T voltage with intermediate voltage phase S Compared to a 2-level drive, there is less voltage change per switch operation, consequently reducing motor terminal surge voltage and leakage current

Figure 2: Sample AC7 Matrix Converter PWM Waveform

Figures 3a and 3b below show the surge voltage created by a

conventional 2-level drive (Figure 3a) and the AC7 Matrix

Converter (Figure 3b) The distance between the motor and

drive is 328 ft (100 m) The AC7 Matrix Converter

suppresses surge voltage by 20 to 50%

Figures 3a and 3b: Surge Voltage Waveforms at the

Motor Terminals (328 ft (100 m) of Motor Cable)

2.2 Input current control

The AC7 Matrix Converter can use all three input phases in PWM switching to control output voltage and input current [3] This is also possible during regenerative operation, combining the merits of being able to suppress power supply harmonics through current control as well as saving energy through regeneration The power factor is about 1 while motoring and about -1 during regenerative operation Figures 4a and 4b show the input line voltage and current waveforms during motoring and regenerative operation Figure 5 shows the input current harmonic wave ratio and distortion, indicating that total harmonic distortion (THD) during both motoring and regenerative operation is kept to no more than 7%, thus providing excellent input current control

Figures 4a and 4b: Input Voltage and Current Waveforms

Figure 5: Harmonic Wave Ratio and Input Current Distortion

(3a) Conventional 2-level Drive

(3b) AC7 Matrix Converter

(4a) During Motor Operation

(4b) During Regenerative Operation

3 Product Outline

3.1 Product Specifications

Major specifications for the AC7 Matrix Converter are given in

Table 1 with product photos shown in Figure 6

Table 1: AC7 Matrix Converter Product Specifications

Figure 6: AC7 Appearance

3.2 Major Features

This section introduces the key differences between the AC7 Matrix Converter and conventional drives

(1) Power Supply Harmonics Without any special devices, the AC7 input current THD is 7% maximum, and has a minimum input power factor of 98% (2) Line Regeneration

The AC7 is fully regenerative which greatly improves system efficiency and reduces the need for additional components (3) Prolonged Life

There are no electrolytic capacitors or other short-lived components in the main circuit, providing a long high-performance life

(4) Reduced Motor Shaft Potential The switching waveform is equivalent to 3-levels, making it possible to reduce motor potential, a major cause of bearing fluting electro-corrosion

(5) No Low-Speed De-rating Current is not concentrated in specific devices, eliminating the need for current de-rating during low-speed operation

4 Conclusion

The range of applications for motor drive technology has spread to almost all industries, leading to increased demand for energy conservation, power supply harmonic reduction, and motor friendliness The AC7 Matrix Converter is the latest Yaskawa innovation in these areas

Applicable Motor Output (HP) 7.5 HP 15 HP 30/40 HP

200/208/220 Vac, 50/60 Hz, 3-phase 380/400/415/440/460/480 Vac, 50/60 Hz, 3-phase

Rated

Output

Output Frequency 120 Hz maximum

Allowable Frequency

Fluctuation

Allowable Voltage Fluctuation +10% to -15%

Output Voltage Input Voltage x 0.93

(Maximum average output voltage) Control Method Sine-wave PWM

Control Modes V/f, Open-loop Vector,

Closed-loop Flux Vector Carrier Frequency 4, 8, or 12 kHz

Power Rating 100% continuous operation across

entire range Overload Capacity 150% rated output for 1 minute

Allowable Power Supply

Frequency Fluctuation

±3% or less, Frequency Fluctuation Ratio: 1 Hz / 100 ms or less

Input Current Control Sine-wave supply; regenerative

Input Harmonics Input current THD 7% or less, input

power factor 98% or more (at rated load) Momentary Power

Loss Compensation

Stops at 15 ms outage or more (factory setting) Up to 2 second ride-through possible with parameter setting.

Conversion Efficiency 97% or more

Height (H) 20.87" 22.05"

Width (W) 11.81" 14.17"

Dimensions

Depth (D) 11.42" 11.89"

Weight (lbs.) 64 110

Input Power Ratings

±3% (Frequency Fluctuation Rate:

1 Hz / 100 ms or less)

(a) 15 HP (b) 30/40 HP

References:

[1] Venturini, M., "A new sine wave in sine wave out conversion technique which eliminates reactive elements," in Proc Powercon 7, 1980, pp E3-1-E3-15

[2] Watanabe, Ishii and Yamamoto, "Motor Drives Using Matrix Converter Technology" (in Japanese), Yaskawa Technical Review, Vol 64, No 247, P 111 (2000, No 2)

[3] J-K.Kang, H.Hara, et al., "The Matrix Converter drive performance under abnormal input voltage conditions," IEEE Trans Power Electronics, Vol 17, No 5, pp 721-730 (Sept., 2002)

[4] Hara, Yamamoto, Sonoda, "Matrix Converter Drive Varispeed AC", Yaskawa Technical Review, Vol 69, No 2,

Serial No 267 (2005)