Design of Active Noise Control System in Automobile Based on DSP

The basic idea of ​​active noise control was first proposed by German physicist Paul Lueg when he invented the "electronic muffler" in 1936. Compared with traditional passive control, active noise control technology has the advantages of obvious control effect on mid- and low-frequency noise, light system, strong real-time performance, etc., and has potential engineering application value.

Noise control is real-time control, which requires a large amount of calculation and is difficult to achieve with ordinary single-chip microcomputers. In the 1980s, the advent of digital signal processing (DSP) chips opened up a broad space for the development of real-time signal control. With the continuous maturity and development of chip technology, DSP has become the core component of modern intelligent controllers.

This paper uses the DSP chip TMS320F2812 to design an intelligent controller that can run independently offline and can be simulated online through a USB interface. An active intelligent control system for automotive interior noise is designed with this controller as the core.

Circuit Design of Intelligent Control System

1 Design process and system block diagram

The design process of the intelligent control system for automobile interior noise is shown in Figure 1.

Figure 1 DSP intelligent controller hardware design flow chart

When selecting devices, we need to consider the compatibility between devices, as well as the supply capacity and technical support of the devices. The performance of the DSP chip TMS320F2812 selected in this design is as follows: it adopts high-performance static CMOS low-power design technology, the main frequency is up to 150MIPS (clock cycle 6.67ns), supports JTAG boundary scan interface; efficient 32-bit high-precision CPU; and has a maximum of 128K×16 FLASH memory, etc.

The design of circuit boards requires knowledge of transmission line theory as well as wiring technology and system structure design to ensure signal integrity, and also focuses on electromagnetic interference and electromagnetic compatibility issues.

As shown in Figure 2, the intelligent controller is mainly composed of analog circuit part (including digital signal acquisition circuit and output signal processing circuit), DSP subsystem (including DSP chip and peripheral circuit), power supply, clock and reset circuit, etc. The design of several main circuits will be introduced below.

Figure 2 Intelligent controller structure diagram

2 Power supply and reset circuit design

The DSP system has high requirements on the performance of the power supply (such as ripple, power-on sequence, etc.), so the linear voltage regulator circuit chip TPS767D301 is selected in this design. TPS767D301 is a dual-output low-leakage voltage regulator with the following features: each power supply output has a separate reset and output enable control; it has a fast transient response function; the voltage output is 3.3V/1.8V adjustable.

The power supply circuit composed of TPS767D301 introduces +5V voltage from an external regulated power supply. After passing through TPS767D301, the output voltage of +5V voltage is 1.8V and 3.3V. In order to reduce the interference of the power supply itself to the DSP, a filtering network is added to the circuit, as shown in Figure 3.

Figure 3 Power supply and reset circuit

3 A/D and D/A circuit design

The TMS320F2812 chip has a 12-bit ADC with a conversion frequency of 25MHz. Its front end is two 8-to-1 multiplexers and two simultaneous sample/hold devices. When the requirements are not very high, it can be used to form a synchronous sequential sampling circuit, or to add an external sample/hold device to form synchronous sampling. Considering the high requirements of the power acquisition accuracy and speed of this system, the external six-channel 16-bit ADC ADS8364 is selected in the sampling module. The device includes 6 high-speed sample-hold amplifiers, 6 high-speed ADCs, a reference voltage source and 3 reference voltage buffers. It can provide a synchronous sampling rate of 250KSPS and can also provide conversion of all 6 input channels with ultra-low power consumption (69mW/per channel), so that the unit cost of all channels is low. The data output interface voltage of the 6 channels is between 2.7 and 5.5V, which is convenient for direct interface with DSP and eliminates the intermediate level conversion. The 6 completely independent ADCs can greatly improve the parallel processing speed of the entire hardware, and can still guarantee an excellent common-mode rejection capability of more than 80dB under a 50kHz input signal, which is particularly suitable for high-interference environments. Figure 4 shows the interface circuit between ADS8364 and TMS320F2812.

In order to realize the control function of the system, the four-channel 12-bit voltage output DAC TLV5614 is selected in the D/A conversion circuit. It has a flexible four-wire serial interface and can be seamlessly connected with TMS320 SPI, QSPI and Microwire serial ports. The programming control of TLV5614 consists of 16-bit serial words, namely two DAC addresses, two independent DAC control bits and 12-bit DAC input values. The device is powered by dual power supplies: one set is the digital power supply for the serial interface, namely DVDD and DGND; the other set is the analog power supply for the output buffer, namely AVDD and AGND. The two sets of power supplies are independent of each other and can be any value between 2.7 and 5.5V. The advantage of dual power supply application is that the DAC uses a 5V power supply, while the digital part of the DAC uses a 2.7-5.5V power supply, which can be connected to a variety of interfaces.

Figure 4 Interface circuit between ADS8364 and TMS320F2812

Figure 5 TLV5614 interface circuit

In the design, the D/A circuit uses a reference voltage of 2.5V. For the convenience of control, the GPIOB of TMS320F2812 is used as the conversion chip control line when controlling the D/A. The circuit is shown in Figure 5.

4 External SRAM, FLASH expansion circuit design

Since the control system needs to store a large amount of data for analysis and utilization, according to the "zero wait" principle between DSP and external memory, IS61LV6416-12T is used to expand the external memory of F2812. IS61LV6416-12T is 64K×16 high-speed CMOS SRAM, powered by 3.3V. Its interface circuit with TMS320F2812 is shown in Figure 6.

Figure 6 External memory expansion circuit

Design of an Active Control Experimental System for Automobile Interior Noise

This control experiment system mainly consists of four parts: the vehicle controlled system model (including actuators), external sound source, controller and signal monitoring (including sensors), as shown in Figure 7. One point that needs to be explained is that in the control system, the controlled vehicle model contains multiple aluminum plates, and only one of them is drawn here for the convenience of expression.

In the experimental system, an external speaker is used to simulate the excitation of the cabin from the outside. The sound waves emitted by the speaker force a surface of the car model composed of aluminum plates to vibrate, causing a large noise inside the car; when the sound pressure sensor placed at a specified position inside the box detects the sound pressure change at that location, it transmits the latest sound pressure value to the DSP controller. The controller makes a timely judgment based on the input and output of the system at this time and exerts control on the system. This control function is completed by the PZT actuator pasted on the thin aluminum plate wall of the closed cabin, because PZT can generate vibration energy under the action of the control signal, which also causes the aluminum plate to vibrate, thereby reducing the noise at the specified position inside the car.

Figure 7 Schematic diagram of experimental system composition

1. Automobile controlled system model

Since this design is aimed at the interior noise of the car, a rough car model is used as the controlled object for the convenience of research. The four sides of the model are composed of 1mm aluminum plates, and control sensors are installed on and inside the car body. The actuator of the control system is PZT, which is symmetrically installed on the model.

Since piezoelectric ceramics have the ability to convert electrical energy into mechanical energy, when the application system energizes the piezoelectric ceramics, the spontaneous dipole moment of the material changes, thereby changing the size of the material. This effect can produce a displacement of 50μm within 20ms. The response speed is unmatched by other materials, and the frequency band is very wide and insensitive to temperature. As the number of pressurization increases, the performance tends to be stable, and it is easy to integrate, which is a necessary material for high-precision and high-speed drives. This design uses piezoelectric material PZT as the actuator.

2 External sound sources

The external sound source in the experiment is replaced by a loudspeaker, which is driven by a signal from a signal generator through a power amplifier.

3 Intelligent Controller

The intelligent controller with TMS320F2812DSP chip as the core can run independently offline and can also be simulated online through the USB interface.

4 Signal Monitor

In order to monitor the control error signal and piezoelectric drive signal in the box and perform signal processing, the signal monitor of this control system adopts a self-developed multifunctional signal acquisition and processing system.

The piezoelectric material of the seat sensor used in this design is piezoelectric film PVDF, and the signal sensed by PVDF is used as the reference signal of the system. PVDF is very thin, soft, low in density and highly sensitive, and its mechanical flexibility is 10 times higher than that of piezoelectric ceramics. The piezoelectricity of PVDF piezoelectric material is 3 to 5 times higher than that of quartz, and the piezoelectric coefficient is higher, so it can be attached to the surface of objects.

in conclusion

Based on TMS320F2812 DSP, this paper designs an intelligent controller that can run independently offline and can be simulated online through USB interface. And with this controller as the core, an active intelligent control experimental system for automobile interior noise is designed. Through theoretical analysis, the control system has high data processing capability and processing speed, so it can play an important role in real-time control.