Design of high-speed motor driver based on IM828-XCC

As modern machine tools develop towards high speed and high precision, the technical requirements for machine tool spindles are getting higher and higher. As one of the important components of high-speed machine tools, the electric spindle can effectively improve the dynamic balance of machine tools and avoid vibration and noise due to its high speed, small size and excellent dynamic performance. The spindle motor is placed in the spindle unit of the machine tool and directly drives the load. Therefore, the traditional mechanical drive structure is simplified and "zero drive" is achieved. Due to the wide application of electric spindles, the motor spindle system is being driven to develop towards high precision, high speed, low energy consumption, high efficiency and high reliability, and has become a hot research topic in countries around the world.

In the trend of modern electric spindle and shaft integration, in order to achieve the requirements of high speed and miniaturization, the copper loss of induction motor will increase, resulting in overheating and severe wear, leading to insufficient motor performance. With the development of permanent magnet synchronous motor, high-speed permanent magnet synchronous electric spindle is more and more widely used. Compared with traditional asynchronous induction motor, high-speed permanent magnet synchronous electric spindle has the advantages of high power factor, small size and high efficiency, which is provided by permanent magnet to provide air gap magnetic field. It has a wide range of applications and development prospects in the fields of high-speed grinding system, high-speed centrifugal air compressor, etc.

High-Speed ​​Permanent Magnet Synchronous Motor (HSPMSM) usually refers to a motor with a rated speed exceeding 10,000 r/min or a difficulty coefficient (the product of speed and square root of power) in the range of (1~10)×105r/min√kw. Its control performance determines the system's working efficiency, operating stability, life and reliability, and the control characteristics also depend on the circuit design and the performance of the power semiconductors in the driver. In particular, the introduction of SiC inverter technology has made great progress in the performance of HSPMSM drivers.

This article will introduce a high-speed motor driver based on IM828-XCC built by Wang Jianyuan's research group at the School of Electrical Engineering of Xi'an University of Technology. It is used to drive a high-speed spindle motor with a rated speed of 15000r/min and a rated power of 2.2kW to achieve high-performance control of the high-speed motor. It has the characteristics of high power density, high efficiency and low heat dissipation.

The main functions of the high-speed permanent magnet synchronous motor drive control system designed in this project are: to realize the sampling, processing and control of signals such as current and voltage; to realize the closed-loop control of the speed of the high-speed permanent magnet synchronous motor without sensor; to realize the monitoring of relevant data such as the speed, stator current, voltage, operating temperature of the power device of the motor's operating status, so as to facilitate the inspection and subsequent maintenance of the motor's operating status.

The high-speed permanent magnet synchronous motor drive control system requires the motor to start smoothly, have a stable speed and a wide adjustable speed range. The technical indicators of the drive control system designed based on the main parameters of the high-speed permanent magnet synchronous motor are as follows:

1

CIPOS Maxi IM828 Introduction

High-speed motors have higher requirements for corresponding drive technologies due to their high speed and high base frequency. If the switching frequency is too low, the output voltage waveform of the driver will be of poor quality. As the speed increases, the control delay and time delay will also increase, thus affecting the control accuracy. The high-speed motor driver designed and built in this project uses the IM828-XCC produced by Infineon Technologies, which uses SiC MOSFET to form a bridge unit with excellent thermal conductivity and is suitable for industrial applications such as industrial drive and motor control. The use of silicon carbide technology makes it the best choice in the field of high-speed motor drive.

IM828-XCC is divided into the following functional units:

1

Inverter part: The three-phase inverter using 1200V CoolSiC Mosfet is combined with an optimized 6-channel SOI gate driver, which has excellent electrical performance. The inverter unit using CoolSiC has low conduction loss and excellent switching characteristics.

2

Protection features: Overcurrent shutdown, built-in NTC thermistor for temperature monitoring, undervoltage lockout for all channels, low-side source pin for all phase current monitoring, all 6 switches are closed during protection.

3

Other features: Allows negative VS potential up to -11V, used for VBS=15V signal transmission, integrated bootstrap function.

Figure 1: IM828-XCC device internal block diagram and device image

2

Driver design

In order to fully demonstrate the excellent performance and outstanding features of IM828, a 4.0kW driver is designed. Figure 2 shows the control board part, and Figure 3 shows the power board part.

Figure 2: Location of main components of the control section

Figure 3: Location of main components in the power section of the drive controller

In order to verify the performance of the driver board, the influence of the switching characteristics of the IPM on the operation of the motor under different working conditions was tested. The platform was powered by a three-phase voltage regulator. The controlled motor was a high-speed spindle motor developed by YSA, Italy. The specific parameters of the motor are shown in Table 1. The motor control mode is speed FOC. Figure 4 shows the dv/dt of the W-phase bridge arm switch tube of the IPM.

Table 1 High-speed motor parameters

Experimental condition 1

Under no-load operating conditions, performance tests were carried out under fs of 20kHz and fs of 60kHz.

Figure 4: fs = 20kHz IPM

The dv/dt of the W-phase bridge arm switch turning off

According to the test waveform, the dv/dt of the upper tube when turned off is 2809V/us, and the dv/dt of the lower tube is 3025V/us. At the same time, the turn-on and turn-off delays of the IPM are tested, and the test results are shown in Figure 5. The drive signal delay from MCU to IPM is tested, and the test results are shown in Figure 6.

Figure 5: Turn-on and turn-off delays of an IPM with fs = 20kHz

Figure 6: fs=20kHz CPU to IPM drive signal delay

At the same time, in order to reflect the characteristics of IPM_828-CXX at high switching frequency, relevant waveforms were also collected at a switching frequency of 60kHz. Figures 7-9 show the dv/dt when the W-phase bridge arm switch is turned off at fs=60kHz, the turn-on and turn-off delays of the IPM, and the drive signal delay from MCU to IPM.

Figure 7: dv/dt of the W-phase bridge arm switch turn-off of the IPM with fs=60kHz

Figure 8: Turn-on and turn-off delays of an IPM with fs = 60kHz

Figure 9: fs=60kHz CPU to IPM drive signal delay

Experimental condition 2

The motor is started at no-load with a given speed of 1000r/min. During stable operation, a full load of TL=1.75Nm is suddenly applied, and the switching frequency is fs=30kHz. The phase current of the motor is shown in Figure 10, where (a) is the current waveform during no-load operation, and (b) is the current waveform during full-load operation. It can be seen that when the motor is running at no-load, the output current fluctuates around 0A; when the motor is running at full load, the output current is stable. The experimental results also verify that the experimental platform designed and built in this project has good driving performance.

(a) Current waveform at no load

(b) Current waveform at full load

Figure 10: Current waveform of the motor under sudden load

At this time, the dv/dt waveform of the W-phase bridge arm in the IPM is as follows:

(a) dv/dt when MOS tube is turned off

(b) dv/dt when the MOS tube is turned on

Figure 11: dv/dt of the W-phase upper bridge arm when turning off and on

(a) dv/dt when MOS tube is turned off

(b) dv/dt when the MOS tube is turned on

Figure 12: dv/dt of the lower tube of the W-phase bridge arm when it is turned off and on

Table 2 dv/dt of the W-phase bridge arm MOS tube inside the IPM at full load

When the motor system runs stably for 15 minutes, the temperature near the chip is measured to be 40.6°C with a handheld temperature tester at an ambient temperature of 21°C.

3

System design points and experience sharing

1

Hardware driver protection adjustment

Figure 10: Hardware driver protection conditioning circuit diagram

The hardware drive protection conditioning circuit has the following protection functions:

MCU reset;

Busbar overvoltage;

Busbar overcurrent;

IPM reset signal (VDD undervoltage, ITRIP overcurrent);

Enable_PWM。

When a fault occurs, the PWM-/EN pin outputs a high level and the 74LVX4245 stops outputting; when normal, the pin outputs a low level.

2

Radiator Design

The high-speed motor drive controller is small in size and high in power. How to quickly dissipate heat is also one of the difficulties in the overall design. According to the design principle shown in Figure 11, considering the position of IPM_IM828-XCC, it is necessary to add pads to the IPM and the rectifier bridge. The IPM pad is to ensure the creepage clearance and safety distance between the IPM and the heat sink.