Hitachi Ltd.

Using an Advanced Sine-wave Drive Technique to Achieve Efficient Motor Control

The advanced motor drive solution for three-phase synchronous motors is called the "ECN3900." It consists of Hitachi's single-chip, high voltage inverter IC teamed with a Renesas R8C/24 group microcomputer. It has software for motor speed control and current phase control (see Figure 3).

Among the reasons that Hitachi chose the R8C/Tiny series microcomputer were the device's low cost and the fact that it came pre-equipped with motor control functions, including a precision oscillator, three-phase timer, and power-on reset function. "The two chips in the ECN3900 have a synergistic functional relationship. The R8C/24 microcomputer generates the clock signal to the inverter IC, while the inverter IC supplies 5V DC power to the R8C/Tiny chip," Mr. Hasegawa said.

The ECN3900's design eliminates the need for external components such as a clock IC and power supply IC, and allows the use of an inexpensive single-sided printed circuit board. "The component count would be much higher if we used logic ICs (for 180-degree operation). Also, these types of products often require double-sided circuit boards. Being able to use a single-sided board is an important factor in keeping the cost down," explained Mr. Hasegawa.

As previously mentioned, in developing the ECN3900 motor control solution, Hitachi's engineers devised their own sine-wave drive technique for inverter control of the motor ― one that is independent of the motor parameters(e.g.R,L,Ke) ^* and can be implemented on the low-cost R8C/24 group microcomputer. Because the solution is independent of the motor parameters(e.g.R,L,Ke) ^* , it is suitable for an expanded range of applications that use different types of motors.

In the area of motor control technology, the ECN3900 solution represents a significant breakthrough. Although high efficiency and low noise levels are typical characteristics of sine-wave drives for permanent magnetic synchronous motors, the control algorithms now used to implement the drives are complex. Typically they require the use of a 32-bit-class microcomputer. Also, the control systems have to be tuned for different motors because the method relies on the motor parameters(e.g.R,L,Ke) ^* for each type. Hitachi's ECN3900 solution, however, eliminates these problems by using a unique control scheme. The microcomputer reads two phases of the position-sensor signals from the motor and one phase of the current-polarity signal generated inside the inverter IC (using a new technique). Making calculations from this data, it controls the phase difference between the current and back EMF in a way that maximizes motor efficiency.

Hitachi plans to release a series of new models that extend the range of motors that the ECN3900 can control. To further increase cost-performance, the company will investigate using R8C/Tiny series microcomputers that have reduced functionality.

^* R : Resistance, L : inductance Ke : back EMF