CN109459618B - Quasi-online capacitance value detection method for direct-current bus capacitor of electric automobile electric drive system - Google Patents

Quasi-online capacitance value detection method for direct-current bus capacitor of electric automobile electric drive system Download PDF

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CN109459618B
CN109459618B CN201811367644.9A CN201811367644A CN109459618B CN 109459618 B CN109459618 B CN 109459618B CN 201811367644 A CN201811367644 A CN 201811367644A CN 109459618 B CN109459618 B CN 109459618B
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CN109459618A (en
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张超
杜博超
崔淑梅
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Harbin Institute of Technology
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Abstract

A quasi-online capacitance value detection method for a direct current bus capacitor of an electric automobile electric drive system belongs to the field of direct current bus capacitor health state monitoring, and solves the problem that the existing electrolytic capacitor health state monitoring method is not suitable for the direct current bus capacitor of the electric automobile electric drive system. The quasi-online capacity value detection method comprises the following steps: in the temporary stop period of the electric automobile in the driving process, a low-frequency alternating current signal doped with a direct current component is injected into a direct shaft of the permanent magnet synchronous motor. And reconstructing a direct current bus capacitance current signal according to the three-phase current signal of the permanent magnet synchronous motor, the inverter IGBT switch signal and a bus current signal at the direct current side of the inverter. And extracting the voltage signal of the direct current bus, filtering out direct current components in the voltage signal and filtering out direct current components in the capacitance current signal of the direct current bus. And performing phase shift on the direct current bus voltage signal and the direct current bus capacitance current signal after the direct current component is filtered, and calculating the capacitance value of the direct current bus capacitance according to the phase-shifted signals.

Description

Quasi-online capacitance value detection method for direct-current bus capacitor of electric automobile electric drive system
Technical Field
The invention relates to a capacitance value detection method of a direct current bus capacitor, and belongs to the field of direct current bus capacitor health state monitoring.
Background
In recent years, with the rapid popularization of electric vehicles, the safety and reliability of electric vehicles are receiving more and more attention. The electric drive system is the main power source of the electric automobile, and the safety and the reliability of the electric drive system directly influence the safe operation of the whole automobile. The direct current bus capacitor is an important part of an electric drive system and is a weak link in a power electronic system. Failure of the dc bus capacitor can lead to degradation of the performance of the electric drive system and, in severe cases, even to a crash of the electric drive system. Therefore, monitoring the health state of the direct current bus capacitor of the electric automobile electric drive system is one of important means for improving the safety and reliability of the electric drive system and ensuring the safe operation of the whole automobile.
The existing capacitor health state monitoring method mainly aims at the electrolytic capacitor, and the method uses the equivalent series resistance value of the electrolytic capacitor to evaluate the health state of the electrolytic capacitor. However, in order to improve the reliability of the system, the dc bus capacitor of the conventional electric drive system generally adopts a thin film capacitor with higher reliability, and the correlation between the health state of the thin film capacitor and the resistance value of the equivalent series resistor is not high, and is highly correlated with the capacitance value of the thin film capacitor. Therefore, the existing capacitor health state monitoring method is not suitable for the direct current bus capacitor of the electric automobile electric drive system.
Disclosure of Invention
The invention provides a quasi-online capacitance value detection method for a direct current bus capacitor of an electric automobile electric drive system, aiming at solving the problem that the existing method for monitoring the health state of an electrolytic capacitor is not suitable for the direct current bus capacitor of the electric automobile electric drive system.
The quasi-online capacity value detection method comprises the following steps:
step one, in the temporary parking period in the driving process of the electric automobile, injecting a low-frequency alternating current signal doped with direct current components into a direct shaft of the permanent magnet synchronous motor;
reconstructing a bus output current signal at the load side of the inverter according to the three-phase current signal of the permanent magnet synchronous motor and the IGBT switching signal of the inverter, and reconstructing a direct current bus capacitance current signal according to the bus output current signal at the load side of the inverter and the bus current signal at the direct current side of the inverter;
extracting a direct-current bus voltage signal through a first-order high-pass filter, filtering a direct-current component in the direct-current bus voltage signal through a first second-order generalized integrator, and filtering a direct-current component in a direct-current bus capacitance current signal through a second-order generalized integrator;
step four, phase shifting is carried out on the direct current bus voltage signal after the direct current component is filtered through a third second-order generalized integrator and a fourth second-order generalized integrator, and phase shifting is carried out on the direct current bus capacitance current signal after the direct current component is filtered through a fifth second-order generalized integrator and a sixth second-order generalized integrator;
and step five, calculating the capacitance value of the direct current bus capacitor according to the output signals of the third second-order generalized integrator to the sixth second-order generalized integrator.
Preferably, the first step is to modify the current controller of the permanent magnet synchronous motor from a PI controller to a PIR controller by introducing a proportional resonant controller into a direct-axis current loop of the permanent magnet synchronous motor, and to inject a low-frequency alternating current signal doped with a direct-current component into the current controller;
the expression of the low frequency alternating current signal doped with a direct current component is:
Figure BDA0001869009040000021
in the formula (I), the compound is shown in the specification,
Figure BDA0001869009040000022
for low-frequency alternating current signals doped with a direct current component, I0Is the amplitude of the DC component, IhAnd ωhAmplitude and frequency, I, respectively, of the low-frequency alternating current signal0＞Ih＞0；
The expression for the PIR controller is:
Figure BDA0001869009040000023
in the formula, Gc(s) PIR controller, Kp、KiAnd KcAre all control parameters of the PIR controller.
Preferably, the expression of the bus output current signal on the load side of the inverter reconstructed in the second step is as follows:
Figure BDA0001869009040000024
in the formula iLFor outputting current signals, U, to the load-side busbar of the inverterhIs the amplitude of the direct-axis alternating voltage signal of the permanent magnet synchronous motor,
Figure BDA0001869009040000025
is the power factor angle, R is the resistance of the phase resistor of the permanent magnet synchronous motor, udcIs a dc bus voltage signal.
Preferably, the expression of the dc bus capacitance current signal reconstructed in step two is as follows:
icap＝idc-iL
in the formula icapIs a DC bus capacitance current signal idcIs the bus current signal on the dc side of the inverter.
Preferably, the first second-order generalized integrator takes the dc bus voltage signal as its input signal, and outputs the dc bus voltage signal with a frequency of 2 ωhThe alternating current component of (a);
the second-order generalized integrator takes the direct current bus capacitance current signal as an input signal thereof, and outputs the frequency of the direct current bus capacitance current signal to be 2 omegahThe alternating current component of (a);
the third second-order generalized integrator and the fourth second-order generalized integrator enable the frequency of the direct-current bus voltage signal to be 2 omegahAs its input signal;
the fifth second-order generalized integrator and the sixth second-order generalized integrator enable the frequency of the direct-current bus capacitance current signal to be 2 omegahAs its input signal.
Preferably, the transfer function of the second order generalized integrator is:
Figure BDA0001869009040000031
where v is the input signal of a second-order generalized integrator, vdAnd vqAre output signals of a second-order generalized integrator, k is a damping coefficient, 0<k<1；
D(s) is adopted by the first second-order generalized integrator, the second-order generalized integrator, the fourth second-order generalized integrator and the sixth second-order generalized integrator as a transfer function;
the third-order generalized integrator and the fifth-order generalized integrator both use q(s) as their transfer functions.
Preferably, step five calculates the capacitance value of the dc bus capacitor according to the following formula:
Figure BDA0001869009040000032
wherein C is the capacitance value of the DC bus capacitor, vq,3、vd,4、vq,5And vd,6Respectively output signals of a third-order generalized integrator to a sixth-order generalized integrator.
The invention relates to a quasi-online capacitance value detection method for a direct current bus capacitor of an electric automobile electric drive system, which is characterized in that a low-frequency alternating current signal doped with a direct current component is injected into a direct shaft of a permanent magnet synchronous motor in a temporary stop period in the driving process of the electric automobile. And reconstructing a bus output current signal at the load side of the inverter according to the three-phase current signal of the permanent magnet synchronous motor and the IGBT switching signal of the inverter, and reconstructing a direct current bus capacitance current signal according to the bus output current signal at the load side of the inverter and the bus current signal at the direct current side of the inverter. The method comprises the steps of extracting a direct-current bus voltage signal through a first-order high-pass filter, filtering a direct-current component in the direct-current bus voltage signal through a first second-order generalized integrator, and filtering a direct-current component in a direct-current bus capacitance current signal through a second-order generalized integrator. And the phase of the direct current bus voltage signal after the direct current component is filtered is shifted through a third second-order generalized integrator and a fourth second-order generalized integrator, and the phase of the direct current bus capacitance current signal after the direct current component is filtered is shifted through a fifth second-order generalized integrator and a sixth second-order generalized integrator. And calculating the capacitance value of the direct current bus capacitor according to the output signals of the third-sixth second-order generalized integrator to the sixth second-order generalized integrator. Therefore, the quasi-online capacitance value detection method for the direct-current bus capacitor of the electric automobile electric drive system can solve the problem that the existing health state monitoring method for the electrolytic capacitor is not suitable for the direct-current bus capacitor of the electric automobile electric drive system.
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The quasi-online capacitance value detection method for the dc bus capacitance of the electric driving system of the electric vehicle according to the present invention will be described in more detail below based on embodiments and with reference to the accompanying drawings, in which:
FIG. 1 is a speed curve diagram of an electric vehicle under a NEDC operating condition according to an embodiment;
FIG. 2 is an equivalent circuit diagram of the capacitor according to the embodiment;
FIG. 3 is a schematic circuit diagram of an electric vehicle motor inverter according to an exemplary embodiment;
FIG. 4 is a graph of the bus output current signal at the load side of the inverter versus the motor phase current signal during a switching cycle according to an exemplary embodiment;
FIG. 5 is a control block diagram of the direct axis of the permanent magnet synchronous motor in the shutdown state according to the embodiment;
FIG. 6 is a schematic circuit diagram of a first order high pass filter according to one embodiment;
FIG. 7 is a block diagram of a second-order generalized integrator according to an embodiment;
fig. 8 shows an example of a second-order generalized integrator where k is 0.01, ωhBode plot at 100 pi;
FIG. 9 is a block diagram of a method for detecting capacitance of a DC bus according to an embodiment;
FIG. 10 shows quadrature axis current i of the PMSM according to the embodimentqIs 0, direct axis current idGiven as I0＝10A，Ih＝9A，ωhDirect axis current i at 30HzdCommand waveform and response waveform diagrams of (1);
FIG. 11 shows quadrature axis current i of the PMSM according to the embodimentqIs 0, direct axis current idGiven as I0＝10A，Ih＝9A，ωhWhen 30Hz idcResponse waveform of (1) andLthe calculated waveform map of (1);
FIG. 12 shows quadrature axis current i of the PMSM according to the embodimentqIs 0, direct axis current idGiven as I0＝10A，Ih＝9A，ωhWhen 30Hz icapThe calculated waveform and the frequency of the direct current bus capacitance current signal after being filtered by the second-order generalized integrator are 2 omegahOf alternating current component icap,2hThe frequency of the voltage signal of the sum direct current bus is 2 omegahAc component u ofdc,2hA waveform diagram of (a).
Detailed Description
The quasi-online capacitance value detection method for the dc bus capacitance of the electric driving system of the electric vehicle according to the present invention will be further described with reference to the accompanying drawings.
Example (b): the present embodiment will be described in detail with reference to fig. 1 to 12.
The quasi-online capacitance value detection method for the direct current bus capacitor of the electric automobile electric drive system is suitable for the electric automobile electric drive system with the direct current bus capacitor being a thin-film capacitor and the motor being a permanent magnet synchronous motor;
the quasi-online capacity value detection method comprises the following steps:
step one, in the temporary parking period in the driving process of the electric automobile, injecting a low-frequency alternating current signal doped with direct current components into a direct shaft of the permanent magnet synchronous motor;
reconstructing a bus output current signal at the load side of the inverter according to the three-phase current signal of the permanent magnet synchronous motor and the IGBT switching signal of the inverter, and reconstructing a direct current bus capacitance current signal according to the bus output current signal at the load side of the inverter and the bus current signal at the direct current side of the inverter;
extracting a direct-current bus voltage signal through a first-order high-pass filter, filtering a direct-current component in the direct-current bus voltage signal through a first second-order generalized integrator, and filtering a direct-current component in a direct-current bus capacitance current signal through a second-order generalized integrator;
step four, phase shifting is carried out on the direct current bus voltage signal after the direct current component is filtered through a third second-order generalized integrator and a fourth second-order generalized integrator, and phase shifting is carried out on the direct current bus capacitance current signal after the direct current component is filtered through a fifth second-order generalized integrator and a sixth second-order generalized integrator;
and step five, calculating the capacitance value of the direct current bus capacitor according to the output signals of the third second-order generalized integrator to the sixth second-order generalized integrator.
In the first step of this embodiment, a current controller of a permanent magnet synchronous motor is modified from a PI controller to a PIR controller by introducing a proportional resonant controller into a direct-axis current loop of the permanent magnet synchronous motor, and injection of a low-frequency alternating current signal doped with a direct-current component is realized by the current controller;
the expression of the low frequency alternating current signal doped with a direct current component is:
Figure BDA0001869009040000051
in the formula (I), the compound is shown in the specification,
Figure BDA0001869009040000052
for low-frequency alternating current signals doped with a direct current component, I0Is the amplitude of the DC component, IhAnd ωhAmplitude and frequency, I, respectively, of the low-frequency alternating current signal0＞Ih＞0；
The expression for the PIR controller is:
Figure BDA0001869009040000053
in the formula, Gc(s) PIR controller, Kp、KiAnd KcAre all control parameters of the PIR controller.
In this embodiment, the expression of the bus output current signal on the load side of the inverter reconstructed in step two is:
Figure BDA0001869009040000054
in the formula iLFor outputting current signals, U, to the load-side busbar of the inverterhIs the amplitude of the direct-axis alternating voltage signal of the permanent magnet synchronous motor,
Figure BDA0001869009040000061
is the power factor angle, R is the resistance of the phase resistor of the permanent magnet synchronous motor, udcIs a dc bus voltage signal.
In this embodiment, the expression of the dc bus capacitance current signal reconstructed in step two is:
icap＝idc-iL
in the formula icapIs a DC bus capacitance current signal idcIs the bus current signal on the dc side of the inverter.
In this embodiment, the first second-order generalized integrator takes the dc bus voltage signal as its input signal, and outputs a frequency of 2 ω in the dc bus voltage signalhThe alternating current component of (a);
the second-order generalized integrator takes the direct current bus capacitance current signal as an input signal thereof, and outputs the frequency of the direct current bus capacitance current signal to be 2 omegahThe alternating current component of (a);
the third second-order generalized integrator and the fourth second-order generalized integrator enable the frequency of the direct-current bus voltage signal to be 2 omegahAs its input signal;
the fifth second-order generalized integrator and the sixth second-order generalized integrator enable the frequency of the direct-current bus capacitance current signal to be 2 omegahAs its input signal.
The transfer function of the second order generalized integrator is:
Figure BDA0001869009040000062
where v is the input signal of a second-order generalized integrator, vdAnd vqAre output signals of a second-order generalized integrator, k is a damping coefficient, 0<k<1；
In this embodiment, the first second-order generalized integrator, the second-order generalized integrator, the fourth second-order generalized integrator, and the sixth second-order generalized integrator all use d(s) as their transfer functions;
the third-order generalized integrator and the fifth-order generalized integrator both use q(s) as their transfer functions.
Preferably, step five calculates the capacitance value of the dc bus capacitor according to the following formula:
Figure BDA0001869009040000063
wherein C is the capacitance value of the DC bus capacitor, vq,3、vd,4、vq,5And vd,6Respectively output signals of a third-order generalized integrator to a sixth-order generalized integrator.
The principle of the quasi-online capacitance value detection method for the dc bus capacitor of the electric drive system of the electric vehicle according to the embodiment is described in detail below.
The method comprises the following steps of (1) carrying out quasi-online fault diagnosis feasibility analysis under the working condition of the electric automobile:
the quasi-online fault diagnosis strategy is an offline diagnosis method for performing fault diagnosis by using the self resources of equipment at the moment of short shutdown of the equipment during operation. The method is mainly used for the application occasions with discontinuous working condition characteristics such as solar energy and wind power generation, and does not need any additional diagnostic instrument. Compared with the traditional offline diagnosis technology, the quasi-online fault diagnosis strategy has the advantages of simplicity in implementation, low cost, high real-time performance and the like. Fig. 1 shows a speed curve of an electric vehicle under NEDC conditions. As can be seen from fig. 1, the operation condition of the electric vehicle is a typical discontinuous operation condition. Therefore, the quasi-online fault diagnosis strategy is very suitable for being applied to electric vehicles.
Failure mechanism and failure characteristics of the thin film capacitor:
the equivalent circuit of the capacitor is shown in fig. 2. In the figure, RESRAnd LESLRespectively an equivalent series resistance and an equivalent series inductance of the capacitor. Because the operating frequency of the direct current bus capacitor is generally low, the equivalent series inductance can be ignored. The electric characteristic of the direct current bus capacitor is determined by the capacitance value and the resistance value of the equivalent series resistor together.
Aluminum electrolytic capacitors and metal film capacitors are two of the most widely used dc bus capacitors. The failure mechanism of the aluminum electrolytic capacitor is that the volatilization of the electrolyte is reduced, and the service life characteristic of the aluminum electrolytic capacitor is generally reflected on the change of the resistance value of the equivalent series resistance. Therefore, most of the fault diagnosis methods for aluminum electrolytic capacitors focus on the problem of detecting the resistance value of the equivalent series resistor.
The metal film capacitor is composed of a metal electrode and a metallized film, and the failure mechanism of the metal film capacitor is completely different from that of an electrolytic capacitor. Failure mechanisms of metal film capacitors can be classified into excessive self-healing, oxidation failure, and open circuit failure. The excessive self-healing is generally caused by manufacturing defects or mechanical damages of the capacitor, and when the fault is serious, the large amount of gas generated by the excessive self-healing can cause the expansion and cracking of the capacitor shell. Oxidative failure is generally caused by a combination of ambient temperature and humidity. The failure of open circuit is caused by the combined action of three stresses of electricity, heat and machinery. When faults caused by the three fault mechanisms occur, the capacitance loss is increased, the temperature of the capacitor is rapidly increased, and the capacitance value of the capacitor is rapidly attenuated. In practical application, the power density of the motor driver of the electric automobile is higher, the heat load is larger, and therefore compared with general industrial application, the occurrence frequency of capacitance faults is higher, and the fault development speed is faster.
From the above analysis, the failure characteristics of the metal film capacitor are related to the loss of capacitance value. The loss of capacitance can be measured by the capacitance loss rate CL, which can be calculated by the following formula:
CL＝(1-C/C0)×100％ (1)
in the formula, C0The initial capacitance value of the capacitor, and C the detection capacitance value of the capacitor.
Normally, the capacitance of the film capacitor decays slowly with use, and when CL > 5%, the film capacitor lifetime can be considered to be exhausted. However, in the vehicle-mounted system, the actual capacitance value detection accuracy is low due to the limitations of factors such as interference and sensor accuracy. If CL > 5% is used as a fault determination condition, the misdiagnosis rate is high. On the other hand, when the thin film capacitance fails, the CL attenuation is much greater than 5%. Therefore, the criterion for determination of the capacitance failure can be relaxed appropriately. In this embodiment, the failure determination principle of the thin film capacitor is as follows: when CL > 10%, the capacitance is determined to be invalid.
According to the formula (1), if the initial capacitance C of the capacitor is known0Therefore, the state monitoring and fault diagnosis of the capacitor can be realized only by detecting the current capacitance value of the capacitor. Therefore, the detection of capacitance value is the basis for realizing the fault diagnosis of the thin film capacitor.
The detection principle of the capacitance value of the direct current bus capacitor is as follows:
the circuit principle of the electric vehicle motor inverter is shown in fig. 3. The motor driver is provided with a current sensor and a voltage sensor on a current bus, and a phase current sensor on the output side of the inverter. In order to realize the detection of the capacitance value of the direct current bus capacitor, a direct current bus capacitor current signal i needs to be detectedcap. However, as the integration of inverters increases and the application of a common bus bar is performed, icapBecomes difficult to measure and requires i to be reconstructed by the IGBT switch tube state and phase current sensorscap。
According to FIG. 3, the DC bus capacitance current signal icapIs expressed as
icap＝idc-iL(2)
In the formula idcIs a bus current signal on the DC side of the inverter, iLAnd outputting a current signal for the bus on the load side of the inverter.
As can be seen from FIG. 3, idcDetectable by a bus current sensor, iLThe measurement can not be directly carried out, but the measurement can be obtained by reconstructing and calculating the phase current of the motor and an IGBT switching signal. FIG. 4 shows a switching cycle iLAnd corresponding relation with the phase current waveform of the motor. I of the present embodimentLTaking the average value of the current integrals of the load sides in one switching period, the calculation formula is shown in fig. 4 as follows:
Figure BDA0001869009040000081
in the formula ia、ibAnd icIs the motor phase current, Ta、TbAnd TcUpper tube conduction time, T, of a three-phase IGBT switching tubesIs a switching cycle.
After the detection of the capacitance current of the direct current bus is solved, the output signal of the inverter needs to be designed, so that the direct current bus generates harmonic components containing capacitance value information. When the permanent magnet synchronous motor stops rotating, a low-frequency alternating current signal is injected into the direct axis of the motor, and the quadrature axis current of the motor is kept to be 0.
The expression of the injected low frequency alternating current signal is as follows:
id＝Ihcosωht (4)
in the formula idFor low frequency alternating current signals, IhAnd ωhRespectively, the amplitude and frequency of the low frequency alternating current signal.
The voltage of a permanent magnet synchronous motor can be expressed as:
Figure BDA0001869009040000082
in the formula udIs a direct-axis alternating voltage signal u of a permanent magnet synchronous motorqIs a quadrature axis AC voltage signal, U, of a permanent magnet synchronous motorhIs the amplitude of the direct-axis alternating voltage signal of the permanent magnet synchronous motor,
Figure BDA0001869009040000091
is the power factor angle.
At this time, the three-phase current and the three-phase voltage of the permanent magnet synchronous motor are respectively:
Figure BDA0001869009040000092
Figure BDA0001869009040000093
Ta、Tband TcThe expression of (c) can be written as:
Figure BDA0001869009040000094
in the formula udcIs a DC bus voltage signal u0And (t) is a zero sequence component injected by the SVPWM modulation strategy.
Substituting formula (6), formula (7) and formula (8) into formula (3), iLThe analytical expression of (a) is:
Figure BDA0001869009040000095
from the above analysis, it can be seen that the bus on the load side of the inverter outputs the current signal iLHas a median existence frequency of 2 omegahThe alternating harmonic component of (a). Meanwhile, due to the filtering effect of the direct current bus capacitor, the voltage and the current of the direct current bus capacitor also have a corresponding existing frequency of 2 omegahThe ripple component of (a). Therefore, the impedance value of the bus capacitor can be approximated by this ripple component, i.e.:
Figure BDA0001869009040000096
in the formula, ZcIs the impedance of the DC bus capacitor, udc,2hFor the frequency of 2 omega in the DC bus voltage signalhAlternating current component of icap,2hThe frequency of the DC bus capacitance current signal is 2 omegahThe alternating current component of (a).
In the middle and low frequency band, the equivalent series resistance of the thin film capacitor is small and can be ignored. Thus, the capacitance can be approximately calculated as:
Figure BDA0001869009040000097
after the capacitance value of the direct current bus capacitor is calculated, CL can be calculated according to the formula (1), and whether the direct current bus capacitor fails or not is judged.
The direct current bus capacitance value detection method based on the second-order generalized integrator comprises the following steps:
according to the analysis, if the capacitance value of the dc bus capacitor is to be detected, two processes of harmonic injection of the motor current, harmonic separation of the dc bus voltage and the dc bus capacitor current are required.
FIG. 5 is a control block diagram of the PMSM straight shaft in a shutdown state, GcAnd(s) is a motor current controller. In order to realize the harmonic injection of the motor current, a proportional resonant controller is introduced into a direct-axis current loop, and a PI controller is modified into a PIR controller, namely:
Figure BDA0001869009040000101
in the formula, Kp、KiAnd KcAre all control parameters of the PIR controller.
If the injected waveform is a pure alternating current component, the injected current respectively corresponds to a magnetizing region and a flux weakening region of the motor in the positive half period and the negative half period, and is influenced by a magnetic saturation effect, so that the waveforms of the magnetizing region and the flux weakening region of the output voltage are not completely symmetrical, and the distortion of the output voltage is caused. Meanwhile, when the alternating current flows through zero, obvious distortion can occur under the influence of IGBT dead time. In order to improve the distortion of voltage and current, the injected current can properly increase the direct current component, so that the injected current always works in a magnetizing region, and each phase current does not cross zero any more, namely:
Figure BDA0001869009040000102
in the formula (I), the compound is shown in the specification,
Figure BDA0001869009040000103
for low-frequency alternating current signals doped with a direct current component, I0Is the amplitude of the DC component, IhAnd ωhAmplitude and frequency, I, respectively, of the low-frequency alternating current signal0＞Ih＞0；
At this time, iLThe analytical expression of (a) is:
Figure BDA0001869009040000104
in the formula, R is the resistance value of the phase resistor of the permanent magnet synchronous motor.
According to the formula (14), when I0When not 0, iLWill contain a significant fundamental component. However, because the current sensor has zero drift error, the error exists between the given direct current component and the actual response of the system, so that I0The measured value of (2) is inaccurate, so the fundamental component cannot be used for detecting the capacitance value of the direct current bus capacitor.
For extraction ofAnd (3) adding a first-order high-pass filter to extract direct-current bus voltage ripples when the direct-current bus voltage is harmonic, and marking the filtered direct-current bus voltage as udc,hf，ChfAnd RhfCapacitance and resistance of the first-order high-pass filter are shown in fig. 6.
In order to realize the separation of harmonic components of the dc bus voltage and the dc bus capacitance current, a second-order generalized integrator is introduced for filtering, and a structural block diagram thereof is shown in fig. 7. The transfer function is:
Figure BDA0001869009040000111
where v is the input signal of a second-order generalized integrator, vdAnd vqAre output signals of a second-order generalized integrator, k is a damping coefficient, 0<k<1；
The k value determines the filtering effect of the second-order generalized integrator, the smaller the k is, the narrower the bandwidth of the second-order generalized integrator is, the better the frequency selection characteristic is, but the response speed becomes slow, and the time for the filter to reach the steady state becomes long. Therefore, the k value should be adjusted appropriately according to actual needs.
A second order generalized integrator is a typical band pass filter. Fig. 8 shows the second-order generalized integrator when k is 0.01, ωhBode plot at 100 pi. As can be seen from the figure, the second-order generalized integrator has a strong frequency selection characteristic, has a strong suppression effect on harmonic waves except for specific frequencies, and is suitable for screening the harmonic waves of the specific frequencies.
In the sampled signal, icapThe direct current bus capacitance value detection circuit contains a direct current component which is mainly derived from zero drift errors of various current sensors, and the zero drift errors can affect the detection accuracy of the capacitance value of a direct current bus capacitor. Therefore, the filter must filter out the dc component of the sampled signal. D(s) and q(s) both enable extraction of harmonic components, but q(s) does not completely eliminate the dc component. Therefore, the present embodiment employs d(s) as a filter for the signal. Meanwhile, after the harmonic separation is completed, the second-order generalized integrator is still used to calculate the effective value of the ac harmonic. The flow of the method for detecting the capacitance of the dc bus is shown in fig. 9. In the figure, D1(s)、D2(s)、Q3(s)、D4(s)、Q5(s) and D6(s) are respectively a first second-order generalized integrator to a sixth second-order generalized integrator,
Figure BDA0001869009040000112
the capacitance value of the dc bus is an approximate calculation value, and this embodiment regards the approximate calculation value as the capacitance value of the dc bus. The third second-order generalized integrator, the fourth second-order generalized integrator, the fifth second-order generalized integrator and the sixth second-order generalized integrator of the embodiment are mainly used for phase shifting, and calculation of u is facilitateddc,2hAnd icap,2hThe amplitude of (c).
Experimental results and analysis:
in order to verify the feasibility of the capacitance value detection method of the direct current bus capacitor, relevant experiments are carried out on an experiment platform. A10 kW permanent magnet synchronous motor is adopted as a prototype in the experiment. The direct current bus capacitor is a metal film capacitor with the model B25620B0557K881, the nominal capacitance value of a single capacitor is 550 mu F, and two capacitors are connected in parallel to serve as a bus supporting capacitor of a motor driving system in an experiment. The main control chip of the electric drive system adopts a DSP chip of TMS320F28335 model, and the interrupt period is 10 k. The model of an AD sampling chip of the system is AD7606, and the sampling precision is 16 bits. The current sensor is model LT 58-S7. In the aspect of setting filter parameters, the capacitance and resistance parameters of the first-order high-pass filter are respectively Chf＝0.1μF、Rhf680k Ω and a cutoff frequency of 2.34 Hz. The parameters of the first second-order generalized integrator to the sixth second-order generalized integrator are kept consistent, and the damping coefficient k is 0.01.
In the experiment, the quadrature axis current i of the permanent magnet synchronous motor is enabledqIs 0, direct axis current idGiven as I0＝10A，Ih9A. FIG. 10 shows ωhWhen 30Hz idCommand waveform and response waveform. From the experimental results, idIs substantially identical to the response waveform, indicating that after the resonant controller is used, idCan follow a reference waveform given by sine, and realizesError-free control of the frequency-injected harmonics is given.
FIG. 11 shows ωhWhen 30Hz idcResponse waveform of (1) andLthe calculated waveform of (2).
FIG. 12 shows ωhWhen 30Hz icapThe calculated waveform and the frequency of the direct current bus capacitance current signal after being filtered by the second-order generalized integrator are 2 omegahOf alternating current component icap,2hThe frequency of the voltage signal of the sum direct current bus is 2 omegahAc component u ofdc,2hThe waveform of (2).
As can be seen from the experimental waveform, a certain DC component I is given0Result in icapA significant fundamental component appears, which is consistent with the theoretical analysis of equation (14). As can be seen from FIG. 12, after filtering by the second-order generalized integrator, the system obtains a more stable icap,2hAnd udc,2hThe waveform and the sine degree are good, and the result shows that the second-order generalized integrator well realizes the filtering function. From the phase of the waveform, icap,2hPhase lead u ofdc,2hThe lead angle is substantially close to 90 deg., which corresponds to the impedance characteristic of the capacitor.
Table 1 gives ωhAnd calculating the system error according to the detection result of the capacitance value of the direct current bus capacitor under different harmonic frequencies and the actual measurement result of the capacitance value of the direct current bus capacitor. The measurement value of the direct current bus capacitance is measured by using an LCR tester, and the corresponding measurement frequency of the LCR is 2 omegah. From the comparison of the measurement result and the detection result, the detection error is about 2%, the detection result is accurate, a data basis can be provided for the fault diagnosis of the metal film capacitor, and the health state of the metal film capacitor can be evaluated.
TABLE 1 capacitance test and measurement
Figure BDA0001869009040000121
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that features described in different dependent claims and herein may be combined in ways different from those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other described embodiments.

Claims (6)

1. The quasi-online capacitance value detection method for the direct-current bus capacitor of the electric automobile electric drive system is characterized in that the quasi-online capacitance value detection method is suitable for the electric automobile electric drive system with the direct-current bus capacitor being a thin-film capacitor and the motor being a permanent magnet synchronous motor;
the quasi-online capacity value detection method comprises the following steps:
step one, in the temporary parking period in the driving process of the electric automobile, injecting a low-frequency alternating current signal doped with direct current components into a direct shaft of the permanent magnet synchronous motor;
reconstructing a bus output current signal at the load side of the inverter according to the three-phase current signal of the permanent magnet synchronous motor and the IGBT switching signal of the inverter, and reconstructing a direct current bus capacitance current signal according to the bus output current signal at the load side of the inverter and the bus current signal at the direct current side of the inverter;
extracting a direct-current bus voltage signal through a first-order high-pass filter, filtering a direct-current component in the direct-current bus voltage signal through a first second-order generalized integrator, and filtering a direct-current component in a direct-current bus capacitance current signal through a second-order generalized integrator;
step four, phase shifting is carried out on the direct current bus voltage signal after the direct current component is filtered through a third second-order generalized integrator and a fourth second-order generalized integrator, and phase shifting is carried out on the direct current bus capacitance current signal after the direct current component is filtered through a fifth second-order generalized integrator and a sixth second-order generalized integrator;
step five, calculating the capacitance value of the direct current bus capacitor according to the output signals of the third second-order generalized integrator to the sixth second-order generalized integrator, and calculating the capacitance value of the direct current bus capacitor according to the following formula:
Figure FDA0002604071040000011
wherein C is the capacitance value of the DC bus capacitor, vq,3、vd,4、vq,5And vd,6Respectively output signals of a third-order generalized integrator to a sixth-order generalized integrator.
2. The quasi-online capacitance value detection method for the direct current bus capacitor of the electric drive system of the electric automobile according to claim 1, characterized in that the method comprises the steps of modifying a current controller of the permanent magnet synchronous motor from a PI controller to a PIR controller by introducing a proportional resonant controller into a direct-axis current loop of the permanent magnet synchronous motor, and injecting a low-frequency alternating current signal doped with a direct current component through the current controller;
the expression of the low frequency alternating current signal doped with a direct current component is:
Figure FDA0002604071040000012
in the formula (I), the compound is shown in the specification,
Figure FDA0002604071040000013
for low-frequency alternating current signals doped with a direct current component, I0Is the amplitude of the DC component, IhAnd ωhAmplitude and frequency, I, respectively, of the low-frequency alternating current signal0>Ih>0；
The expression for the PIR controller is:
Figure FDA0002604071040000021
in the formula, Gc(s) PIR controller, Kp、KiAnd KcAre all PIR controllersThe control parameter of (1).
3. The quasi-online capacitance value detection method for the direct-current bus capacitor of the electric drive system of the electric vehicle as claimed in claim 2, wherein the expression of the bus output current signal on the load side of the inverter reconstructed in the step two is as follows:
Figure FDA0002604071040000022
in the formula iLFor outputting current signals, U, to the load-side busbar of the inverterhIs the amplitude of the direct-axis alternating voltage signal of the permanent magnet synchronous motor,
Figure FDA0002604071040000023
is the power factor angle, R is the resistance of the phase resistor of the permanent magnet synchronous motor, udcIs a dc bus voltage signal.
4. The quasi-online capacitance value detection method for the direct current bus capacitor of the electric drive system of the electric vehicle as claimed in claim 3, characterized in that the expression of the direct current bus capacitor current signal reconstructed in the second step is as follows:
icap＝idc-iL
in the formula icapIs a DC bus capacitance current signal idcIs the bus current signal on the dc side of the inverter.
5. The method for detecting the quasi-online capacitance value of the DC bus capacitor of the electric drive system of the electric automobile according to claim 4, wherein the first second-order generalized integrator takes the DC bus voltage signal as an input signal thereof, and outputs the DC bus voltage signal with the frequency of 2 ωhThe alternating current component of (a);
the second-order generalized integrator takes the direct current bus capacitance current signal as an input signal thereof, and outputs the frequency of the direct current bus capacitance current signal to be 2 omegahThe alternating current component of (a);
third and second order generalized integratorAnd the fourth second-order generalized integrator are used for enabling the frequency of the direct-current bus voltage signal to be 2 omegahAs its input signal;
the fifth second-order generalized integrator and the sixth second-order generalized integrator enable the frequency of the direct-current bus capacitance current signal to be 2 omegahAs its input signal.
6. The method for detecting the quasi-online capacitance value of the direct-current bus capacitor of the electric drive system of the electric automobile according to claim 5, wherein the transfer function of the second-order generalized integrator is as follows:
Figure FDA0002604071040000031
where v is the input signal of a second-order generalized integrator, vdAnd vqAre output signals of a second-order generalized integrator, k is a damping coefficient, 0<k<1；
The method is characterized in that the first second-order generalized integrator, the second-order generalized integrator, the fourth second-order generalized integrator and the sixth second-order generalized integrator adopt D(s) as transfer functions;
the third-order generalized integrator and the fifth-order generalized integrator both use q(s) as their transfer functions.
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