Disclosure of Invention
The basic idea of the present invention is that the technologies for implementing power line communication mainly include Orthogonal Frequency Division Multiplexing (OFDM), Spread Spectrum (SS) and narrowband carrier technologies. Orthogonal frequency division multiplexing and spread spectrum technologies are widely applied to low-voltage power line communication, but the two technologies are complex to implement, use more equipment, have higher cost and have poorer economy when being used in the field of new energy automobiles; the traditional narrow-band transmission technology causes lower reliability of low-voltage narrow-band power line communication because of serious signal attenuation, but has the advantages of simple structure, convenient realization, low cost and the like; compared with low-voltage power line communication, the vehicle-mounted power line communication has the characteristics of direct current transmission, short transmission distance, small noise interference and the like, so that signal transmission by utilizing a narrow-band carrier communication technology in a new energy automobile has certain theoretical feasibility.
One of the purposes of the invention is to provide a BFSK-based vehicle-mounted power line communication system for a new energy automobile, which has the advantages of simple structure, reliable performance and good effect; the BFSK-based vehicle-mounted power line communication method for the new energy automobile is scientific, reasonable, high in applicability and good in economical efficiency.
One of the technical schemes adopted for realizing the purpose of the invention is that a BFSK-based vehicle-mounted power line communication system for a new energy automobile is characterized by comprising the following steps: the system comprises a baseband signal transmitter, a BFSK modulator, a communication channel of a vehicle-mounted power line, a BFSK demodulator and a baseband signal receiver, wherein the baseband signal transmitter, the BFSK modulator, the communication channel of the vehicle-mounted power line, the BFSK demodulator and the baseband signal receiver are electrically connected in sequence.
The second technical scheme adopted for achieving the purpose of the invention is that a BFSK-based vehicle-mounted power line communication method for new energy automobiles is characterized by comprising the following steps: it comprises the following steps:
1) vehicle-mounted power line system design and communication channel model building
Firstly, determining a signal transmission medium of the electric automobile, namely a wire harness material, wherein a copper core and polyvinyl chloride insulation low-voltage wire cable is adopted as an automobile power wire harness, polyvinyl chloride is adopted as an insulation material, a copper core is adopted as a conductor material, and the characteristic impedance of the wire harness is 50 omega;
determining the specification, distance and distribution condition of the electric automobile wire harness according to the electric automobile load condition and the actual automobile body condition;
collecting the load of each electric automobile under different carrier frequencies;
fourthly, determining the channel condition when the baseband signal is transmitted according to the specification, material, distribution and load change condition of the selected wire harness and the formula (1),
wherein c isiRepresents the product of inherent attenuation and multipath fading part of signal in channel, i represents the number of communication paths, N represents the total effective path from the transmitting end to the receiving end, i.e. the number of multipath, tauiThe delay of the ith path is represented, and delta represents a time function for carrying out delay processing on the ith path;
2) acquisition and modeling of vehicle-mounted power line communication channel noise
The noise in the vehicle-mounted power line channel comprises impulse noise and background noise, the impulse noise in the electric vehicle is mainly generated by a DC/DC converter, when the DC/DC converter is started, an MOSFET works to generate the impulse noise, and an impulse noise sampling point in the channel adopts 50MSamples/s, and the expression of the impulse noise is represented by the superposition of a periodic impulse noise formula (2) and a triangular wave formula (3) generated by the MOSFET;
in the formula t
arrIs the time of arrival of the pulse, τ is the width of the pulse,
f is the frequency of a sine wave, or called pseudo frequency, and M represents the amplitude of the impulse noise; t is
DCPeriod of triangular wave, D
DCThe duty ratio of the triangular wave, A is the amplitude of the triangular wave, k represents the harmonic frequency, and a and b respectively represent the amplitude of a cosine component and the amplitude of a sine component;
because the carrier communication frequency of the vehicle-mounted power line is higher, the background noise is approximately replaced by white Gaussian noise;
3) BFSK modulation-demodulation model establishment
A modulation part: gating two carrier frequencies with different frequencies, namely oscillators by using a gate circuit, enabling code elements '1' and '0' in the digital signal to respectively correspond to carrier waves with different frequencies, outputting modulated waveform to be continuous sine waves with different frequencies alternated mutually, and enabling a mathematical expression of the modulated signal to be a formula (4);
in the formula of omega
1、θ
1The angular frequency and the initial phase of the sine wave are respectively output by the
oscillator 1, and s (t) corresponds to the time width of the rectangular pulse after the sine wave is modulated by the
gate circuit 1; omega
2、θ
2The angular frequency and the initial phase of the sine wave are respectively output to the
oscillator 2;
the sine wave is modulated by the
gate 2 to correspond to the time width of the rectangular pulse.
A demodulation part: firstly, the modulated waveform passes through two band-pass filters to obtain two carriers with different frequencies, secondly, the obtained carriers are respectively multiplied with corresponding synchronous coherent carriers, then, the double-frequency signal and high-frequency noise are filtered by a low-pass filter, and finally, the digital baseband signal is restored under the action of fixed sampling pulses;
4) signal transmission process
The first step is as follows: the singlechip sends out a digital baseband signal;
the second step is that: modulating the baseband signal through a modulation part of a BFSK technology;
the third step: the coupler couples the modulation signal into a carrier signal with the inherent high frequency, and then the carrier signal is accessed into a vehicle-mounted power line system;
the fourth step: the decoupler decouples signals transmitted through the vehicle-mounted power system into modulated signals;
the fifth step: demodulating the received signal by a BFSK technique;
and a sixth step: the receiver performs analog-to-digital conversion on the demodulated signal through fixed sampling pulses, converts the demodulated signal into a digital signal, and finally the digital signal controls the load through triggering the power electronic device.
The invention discloses a BFSK-based vehicle-mounted power line communication system and a method thereof for a new energy automobile, and the system and the method are applied to electric automobiles by the power line communication system based on the BFSK technology under the condition of narrow-band transmission of signals. BFSK is used as a modulation and demodulation means of vehicle-mounted power line communication signals, a vehicle-mounted power line system is used as a transmission path of the signals, effective transmission of the signals is achieved, and the purposes of simplifying communication lines, reducing loads and cost and improving the cruising ability of the electric automobile are achieved. The system has the advantages of simple structure, reliable performance, good effect and the like; through simulation analysis, the method can completely realize reliable transmission of signals in the vehicle-mounted power line system, thereby verifying the feasibility and effectiveness of the method. The method has the advantages of being scientific and reasonable, strong in applicability, good in economical efficiency and the like.
Detailed Description
The invention is further illustrated by the following figures and examples.
Referring to fig. 1, the BFSK-based vehicle-mounted power line communication system for the new energy vehicle of the present invention includes: the system comprises a baseband signal transmitter, a BFSK modulator, a communication channel of a vehicle-mounted power line, a BFSK demodulator and a baseband signal receiver, wherein the baseband signal transmitter, the BFSK modulator, the communication channel of the vehicle-mounted power line, the BFSK demodulator and the baseband signal receiver are electrically connected in sequence.
Referring to fig. 1, the BFSK-based vehicle-mounted power line communication method for the new energy automobile of the present invention includes the following steps:
A. vehicle-mounted power line system design and communication channel model building
(1) And determining a signal transmission medium, namely a wiring harness material of the electric automobile. The automobile power wire harness adopts a copper core polyvinyl chloride insulation low-voltage wire cable, the insulation material is polyvinyl chloride, the conductor is made of a copper core, and the characteristic impedance of the wire harness is 50 omega.
(2) And designing and determining the specification, distance and distribution condition of the electric automobile wire harness according to the electric automobile load condition and the actual automobile body condition. For the trunk line, the load is too much to causeThe current-carrying capacity is larger, and the specification of the trunk line is selected to be 0.5mm in cross section according to the specification and condition of the actual power line2The power line bundle of (2) is similar to the power line bundle, and the secondary line is selected to be 0.3mm2And the wiring harness directly connected with the load is selected according to the current-carrying capacity of the load as a whole. The specification, distance and distribution of the specific automobile wire harness are shown in fig. 2.
(3) The load of each electric automobile under different carrier frequencies is collected, the change condition is shown in fig. 3, and the motor is an inductive load and is seriously influenced by the frequency, so the load impedance of the wiper motor changes violently, and the change degree of other impedances is relatively small.
(4) Determining the channel condition of the baseband signal transmission according to the specification, material, distribution and load change condition of the selected wire harness and formula (1), wherein ciRepresents the product of inherent attenuation and multipath fading part of the signal in the channel, i represents the number of communication paths, N represents the total effective path from the transmitting end to the receiving end, and tauiThe delay of the ith path is represented, namely the delay is the number of the multipath, and delta represents a time function for performing delay processing on the i paths;
in order to embody the typicality of the scene, the line length and the on-off state of the load are comprehensively considered, the rear steering lamp, the rear fog lamp, the battery, the rear wiper motor, the rear brake lamp and the rear width indicator lamp are selected, and a communication channel from a vehicle ECU (operation place) to the rear fog lamp is established. The topology of the power system and the overall attenuation of the channels from the operator to the rear fog lamp are shown in fig. 8 and 9.
B. Acquisition and modeling of vehicle-mounted power line communication channel noise
The noise in the vehicle-mounted power line channel mainly includes impulse noise and background noise. Impulse noise in an electric vehicle is mainly generated by a DC/DC converter, and when the DC/DC converter is started, MOSFETs operate to generate impulse noise. The impulse noise sampling point in the channel adopts 50MSamples/s, and the expression can be represented by the superposition of periodic impulse noise (2) and a triangular wave formula (3) generated by an MOSFET;
t in formula (2)
arrRepresenting the time of arrival of the pulse, tau the width of the pulse,
representing the angle of the impulse noise excursion, f is the frequency of the sine wave, or referred to as the pseudo frequency, and M represents the amplitude of the impulse noise. T in formula (3)
DC,D
DCAnd a denotes a period, a duty ratio and an amplitude of the triangular wave, respectively, k denotes a harmonic order, and a and b denote a cosine component amplitude and a sine component amplitude, respectively. Fig. 4 and 5 are time domain and frequency domain graphs of the obtained impulse noise, and as can be seen from the time domain graph of fig. 4, the overall amplitude of the impulse noise is relatively large in fluctuation, but has strong periodicity, and the occurrence point of the noise is located at the transformation time when the triangular wave falls or rises. Similarly, the frequency domain graph of fig. 5 also verifies the strong periodicity of the impulse noise, and as can be seen from fig. 5, the impulse with strong periodicity is prominent in the whole frequency domain, i.e., the impulse noise, and the amplitude of the impulse noise is maximum when the frequency is about 70 KHz.
Due to the fact that the communication frequency of the vehicle-mounted power line carrier is high, the background noise is approximately replaced by white Gaussian noise.
C. BFSK modulation-demodulation model establishment
(1) A modulation part: two carrier frequencies (oscillators) with different frequencies are gated by a gate circuit, so that symbols "1" and "0" in the digital signal respectively correspond to the carrier frequencies with different frequencies. The output waveform after modulation is continuous sine waves with different frequencies alternating with each other. FIG. 6 is a schematic block diagram of a modulation model, the mathematical expression of the modulated signal being shown in equation (4);
(2) a demodulation part: firstly, the modulated waveform passes through two band-pass filters to obtain two carrier waves with different frequencies. Then the obtained carrier is multiplied with the corresponding synchronous coherent carrier, then the double frequency signal and the high frequency noise are filtered by a low pass filter, and finally the digital baseband signal is restored under the action of the fixed sampling pulse. Fig. 7 is a functional block diagram of a modulation model.
D. Signal transmission process
The first step is as follows: the singlechip sends out a digital baseband signal;
the second step is that: modulating the baseband signal through a modulation part of a BFSK technology;
the third step: the coupler couples the modulation signal into a carrier signal with the inherent high frequency, and then the carrier signal is accessed into a vehicle-mounted power line system;
the fourth step: the decoupler decouples signals transmitted through the vehicle-mounted power system into modulated signals;
the fifth step: demodulating the received signal by a BFSK technique;
and a sixth step: the receiver performs analog-to-digital conversion on the demodulated signal through fixed sampling pulses, converts the demodulated signal into a digital signal, and finally the digital signal controls the load through triggering the power electronic device.
Since the coupling and decoupling part is mainly the wave-form conversion in the power line carrier communication system, occasionally the signal will produce little attenuation, and the influence on the signal transmission is little, so the coupling and decoupling part is omitted in the signal transmission system.
Specific examples are as follows: fig. 10 is a schematic diagram of a BFSK-based vehicle-mounted power line communication simulation system which is set up for verifying the feasibility of the method provided by the present invention, and the system includes a baseband signal transmitting part, a BFSK modulating part, a vehicle-mounted power line communication channel part, a BFSK demodulating part and a signal receiving part. The parameter setting is based on a power line carrier communication chip ST7538, the communication speed is set to 4800bps, and the frequency interval of the oscillator is set to 4800 Hz. Then, respectively adding Gaussian white noise, triangular wave noise and mixed noise of the Gaussian white noise and the triangular wave noise into the established vehicle-mounted communication channel, and counting error rate conditions of carrier frequencies of 100KHz, 200KHz, 300KHz, 400KHz and 500KHz respectively.
According to the graphs of fig. 11, 12 and 13, under the condition of the same noise type and the same signal-to-noise ratio, the error rate of the carrier frequency of 100KHz is the minimum, and the communication effect is the best. Analyzing the condition that the carrier frequency is 100 KHz;
as can be seen from the variation curve of Gaussian white noise shown in FIG. 11, when the SNR is 14, i.e. the noise power is 0.025W, the bit error rate is about 0.7%, the reliable transmission of the signal can be basically realized, and the power of the Gaussian white noise only reaches 10 according to the actual measurement-8And the signal-to-noise ratio is about 80, so that the influence of actual white gaussian noise on transmission is basically zero.
As can be seen from the bit error rate simulation result under the influence of impulse noise in fig. 12, when the signal-to-noise ratio is 6 (at this time, the actual impulse noise is enlarged by 29 times), the bit error rate is about 0.7%. Therefore, under the actual impulse noise interference, the BFSK technology can also realize the effective transmission of signals.
In the mixed noise, the actual white gaussian noise power is extremely low and is much lower than the influence of the impulse noise on the vehicle-mounted power line communication channel, so the variation curves of the mixed noise and the impulse noise are basically the same, as shown in fig. 13. Therefore, by integrating the simulation results, the BFSK can meet the information transmission requirement of vehicle-mounted power line communication, the reliable transmission of signals can be realized, and the feasibility of the method is verified.
The detailed description of the present invention is merely exemplary in nature and is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and modifications and variations which will be apparent to those skilled in the art are intended to be included within the scope of the invention.