阅读说明：本技术 一种直流母线电容估算方法及直流母线电容估算装置 (Direct current bus capacitance estimation method and direct current bus capacitance estimation device ) 是由 张品佳 孟天泽 夏科睿 于 2020-03-25 设计创作，主要内容包括：本发明的一个或多个实施例公开了直流母线电容估算方法及直流母线电容估算装置,适用于逆变器驱动系统中,方法包括：在电机的正常工作状态下,在直流母线电容放电过程中,测量直流母线电压以及逆变器输出侧三相电压、三相电流；对直流母线电流进行重构；基于直流母线电压以及重构得到的直流母线电流,采用递归最小二乘法对直流母线电容值进行估算。通过在电机的正常工作状态下测量,避免对电机的正常运行产生干扰,通过选择电容放电区域测量,提高估算结果的有效性,保障逆变器系统的安全可靠运行,通过采用递归最小二乘法估算电容值,提高了估算精度,更适于实际应用。(One or more embodiments of the present invention disclose a dc bus capacitance estimation method and a dc bus capacitance estimation apparatus, which are applicable to an inverter driving system, the method including: under the normal working state of the motor, in the discharging process of the direct current bus capacitor, measuring the direct current bus voltage and the three-phase current of the output side of the inverter; reconstructing a direct current bus current; and estimating the capacitance value of the direct current bus by adopting a recursive least square method based on the voltage of the direct current bus and the direct current bus current obtained by reconstruction. The measurement is carried out under the normal working state of the motor, the interference on the normal operation of the motor is avoided, the effectiveness of an estimation result is improved by selecting a capacitor discharge area for measurement, the safe and reliable operation of an inverter system is guaranteed, the estimation precision is improved by estimating the capacitance value by adopting a recursive least square method, and the method is more suitable for practical application.)

1. A DC bus capacitance estimation method is characterized in that a DC bus is connected with an input end of an inverter, a capacitor is a capacitor between the DC buses, and an output end of the inverter is used for driving a motor; characterized in that the method comprises the following steps:

under the normal working state of the motor, measuring the voltage of a direct current bus, the three-phase voltage and the three-phase current of the output side of the inverter;

reconstructing the direct current bus current according to the three-phase voltage and the three-phase current at the output side of the inverter;

and estimating the capacitance value of the direct current bus by adopting a recursive least square method based on the voltage of the direct current bus and the direct current bus current obtained by reconstruction.

2. The method according to claim 1, wherein the step of estimating the capacitance value of the dc bus by using a recursive least squares method based on the dc bus voltage and the reconstructed dc bus current is specifically estimated by using the following formula:

C(n)＝C(n-1)+k(n)(n)

wherein, C (n) represents the estimated direct current bus capacitance value of the nth sampling point, n is more than or equal to 1, k (n) represents a gain coefficient, and (n) represents an estimation error;

the formula for k (n) is:

wherein, p (n) represents the middle coefficient of the nth sampling point, x (n) represents the change rate of the dc bus voltage value measured by the nth sampling point, and the calculation formula of p (n) is:

P(n)＝P(n-1)-k(n)x(n)P(n-1)，

the formula for x (n) is:v_DC(n) represents the direct current bus voltage value measured by the nth sampling point, and t represents time;

the calculation formula of (n) is: (n) ═ y (n) -C (n-1) x (n),

wherein y (n) represents the reconstructed direct current bus current value measured by the nth sampling point, and the calculation formula of y (n) is as follows: y (n) ═ i_DC(n)。

3. The method according to claim 2, wherein the initial value P (0) is 0.00001, and C (0) is a nominal capacitance value.

4. The method for estimating the capacitance of the direct current bus according to claim 1, wherein the step of measuring the voltage of the direct current bus and the three-phase voltage and the three-phase current of the output side of the inverter comprises the following steps: judging whether the direct current bus capacitor is in a discharging stage; if yes, the next step is carried out, otherwise, whether the direct current bus capacitor is in the discharging stage is continuously judged.

5. The method according to claim 4, wherein the step of determining whether the dc bus capacitor is in a discharging phase comprises:

judging whether the direct current bus capacitor is in a discharging stage by judging whether the direct current bus voltage is in a descending stage, wherein the direct current bus capacitor is in the discharging stage in the descending stage, otherwise, the direct current bus capacitor is not in the discharging stage;

or judging whether the voltage change rate of the direct current bus is smaller than zero to judge whether the direct current bus capacitor is in the discharging stage, if the voltage change rate of the direct current bus is smaller than zero, the direct current bus capacitor is in the discharging stage, otherwise, the direct current bus capacitor is not in the discharging stage.

6. The method according to any one of claims 4 to 5, wherein the step of reconstructing the DC bus current according to the three-phase voltage and the three-phase current at the output side of the inverter comprises:

obtaining the corresponding relation between the direct current bus current and the three-phase current at the output side of the inverter;

and obtaining the switching state of a bridge arm of the inverter according to the three-phase voltage at the output side of the inverter.

7. The method for estimating the capacitance of the direct-current bus according to claim 6, wherein the direct-current bus current at the discharge stage of the capacitance of the direct-current bus is reconstructed by adopting the following expression:

I_dc＝S_a·i_a+S_b·i_b+S_c·i_c

wherein i_a、i_b、i_cFor three-phase current at the output side of the inverter, I_dcRepresenting the reconstructed DC bus current, S_a、S_b、S_cA, B, C, wherein the corresponding switch state is 1 when the upper arm is turned on and 0 when the lower arm is turned on.

8. A dc bus capacitance estimation device for performing the dc bus capacitance estimation method according to any one of claims 1 to 7, wherein the dc bus is a dc bus connected to an input terminal of an inverter, the capacitance is an inter-dc bus capacitance, and the output terminal of the inverter is used for driving a motor; characterized in that the device comprises:

the signal acquisition module is used for measuring the voltage of a direct current bus and the three-phase voltage and the three-phase current of the output side of the inverter under the normal working state of the motor;

and the direct current bus capacitance value calculation module is used for reconstructing the direct current bus current according to the three-phase voltage and the three-phase current at the output side of the inverter and is also used for estimating the direct current bus capacitance value by adopting a recursive least square method based on the direct current bus voltage and the reconstructed direct current bus current.

9. The dc bus capacitance estimation device according to claim 8, wherein the step of estimating the dc bus capacitance value by using a recursive least squares method based on the dc bus voltage and the reconstructed dc bus current is specifically estimated by using the following formula:

C(n)＝C(n-1)+k(n)(n)

wherein, C (n) represents the estimated direct current bus capacitance value of the nth sampling point, n is more than or equal to 1, k (n) represents a gain coefficient, and (n) represents an estimation error;

the formula for k (n) is:

wherein, p (n) represents the middle coefficient of the nth sampling point, x (n) represents the change rate of the dc bus voltage value measured by the nth sampling point, and the calculation formula of p (n) is:

P(n)＝P(n-1)-k(n)x(n)P(n-1)，

the formula for x (n) is:v_DC(n) represents the direct current bus voltage value measured by the nth sampling point, and t represents time;

the calculation formula of (n) is: (n) ═ y (n) -C (n-1) x (n),

wherein y (n) represents the reconstructed direct current bus current value measured by the nth sampling point, and the calculation formula of y (n) is as follows: y (n) ═ i_DC(n)。

10. The dc bus capacitance estimation device of claim 8, wherein the dc bus current at the discharging stage of the dc bus capacitance is reconstructed by the following expression:

I_dc＝S_a·i_a+S_b·i_b+S_c·i_c

wherein i_a、i_b、i_cFor three-phase current at the output side of the inverter, I_dcRepresenting the reconstructed DC bus current, S_a、S_b、S_cA, B, C, wherein the corresponding switch state is 1 when the upper arm is turned on and 0 when the lower arm is turned on.

Technical Field

The invention relates to the field of motors, in particular to the field of inverter driving systems of motors, and particularly relates to a direct-current bus capacitance estimation method and a direct-current bus capacitance estimation device.

Background

For example, motors such as permanent magnet synchronous motors are widely applied in various fields such as electric automobiles, wind power generation and the like, the reliability of a predriver thereof is required to be higher and higher, the reliability of an inverter driving system becomes the most critical problem in a motor system, the reliability of a direct current bus capacitor in the inverter driving system is the most important, the aging state of the direct current bus capacitor in the inverter is monitored in real time, the direct current bus capacitor with defects is found and replaced in time, and the method has important significance for improving the reliability of the inverter. Therefore, it is very critical to be able to accurately and effectively evaluate the health and retrograde motion of the capacitor. There have been many studies on estimation of dc bus capacitance, but most of the techniques of these studies have no way to be applied to the actual industrial field. In practical industrial application, effective evaluation of the capacitance is urgently needed.

At present, the methods for evaluating the health status of the dc bus capacitor are mainly divided into two evaluation methods, i.e., an estimation through an equivalent series resistance and an estimation through a dc bus capacitance. The estimation of the capacitance value of the dc bus can be calculated by using a current formula of the capacitor, so that two variables are required to be obtained: dc bus voltage, dc bus current, and since a voltage current detection device is generally mounted on the inverter side in the inverter driving system of the existing motor, however, the direct current bus has no corresponding sensor, so if the direct measurement of the direct current bus voltage and the direct current bus current needs to be modified to the whole structure, therefore, the difficulty of industrial application is increased, the estimation of the capacitance value of the direct current bus by adopting the existing structure is expected, namely, the existing voltage and current detection device at the inverter side is directly utilized, the direct current bus capacitance value estimation method applied to the inverter driving system in the prior art mainly depends on a high-frequency injection mode, signals obtained by a three-phase current sensor are output by the inverter, and reconstructing the direct current bus current, measuring the direct current bus voltage, obtaining a voltage and current signal of corresponding injection frequency after signal filtering processing, and estimating the direct current bus capacitance and the reverse line. However, the high-frequency injection method is to additionally inject a voltage signal or a current signal with a specific frequency for calculation when the inverter driving system normally operates, and thus belongs to an invasive estimation method.

In addition, the conventional capacitance value estimation method, i.e. the current-voltage equation of the capacitor is used to estimate the capacitance value, the voltage change rate needs to be calculated. However, in the actual industrial field, discrete digital quantity of a computer is used for operation, so that at least two sampling points are needed for calculating the change rate of the solved voltage, when a traditional current-voltage equation is used for estimating the capacitance value, because the operation of each point is relatively independent, a more ideal estimation effect is to be achieved, an extremely high sampling frequency is needed, the operation amount is increased, the burden of control is increased, and the method is not suitable for industrial application, meanwhile, because the capacitance values of the two sampling points are not necessarily completely equal, errors can be caused by the direct time interval of the two sampling points, and the fluctuation of the voltage can cause the error of the voltage change rate, which is the reason that the error can occur when the capacitance value is calculated by each point, if the error cannot obtain the subsequent optimization processing, the error can be directly substituted into the final operation result, the capacitance value cannot be predicted, so that the capacitance value estimation accuracy is not high when the capacitance value is estimated by adopting the traditional current-voltage equation.

Disclosure of Invention

Objects of the invention

In view of this, embodiments of the present invention provide a method and an apparatus for estimating a dc bus capacitance, so as to solve the technical problem of improving the capacitance estimation accuracy while effectively estimating the dc bus capacitance without affecting the stable and normal operation of a motor system.

(II) technical scheme

On one hand, the embodiment of the invention provides a direct current bus capacitance estimation method, wherein a direct current bus is connected with an input end of an inverter, a capacitor is a capacitor between the direct current buses, and an output end of the inverter is used for driving a motor; the method comprises the following steps:

under the normal working state of the motor, measuring the voltage of a direct current bus, the three-phase voltage and the three-phase current of the output side of the inverter;

reconstructing the direct current bus current according to the three-phase voltage and the three-phase current at the output side of the inverter;

and estimating the capacitance value of the direct current bus by adopting a recursive least square method based on the voltage of the direct current bus and the direct current bus current obtained by reconstruction.

Further, the step of estimating the capacitance value of the dc bus by using a recursive least square method based on the dc bus voltage and the dc bus current obtained by reconstruction specifically uses the following formula to estimate:

C(n)＝C(n-1)+k(n)(n)

wherein, C (n) represents the estimated direct current bus capacitance value of the nth sampling point, n is more than or equal to 1, k (n) represents a gain coefficient, and (n) represents an estimation error;

the formula for k (n) is:

wherein, p (n) represents the middle coefficient of the nth sampling point, x (n) represents the change rate of the dc bus voltage value measured by the nth sampling point, and the calculation formula of p (n) is: p (n) ═ P (n-1) -k (n) x (n) P (n-1), and x (n) are calculated by the following formula:v_DC(n) represents the direct current bus voltage value measured by the nth sampling point, and t represents time;

the calculation formula of (n) is: (n) ═ y (n) -C (n-1) x (n),

wherein y (n) represents the reconstructed direct current bus current value measured by the nth sampling point, and the calculation formula of y (n) is as follows: y (n) ═ i_DC(n)。

Further, the initial value P (0) is 0.00001, and C (0) is a capacitance nominal value.

Further, the step of measuring the dc bus voltage and the three-phase current at the output side of the inverter comprises: judging whether the direct current bus capacitor is in a discharging stage; if yes, the next step is carried out, otherwise, whether the direct current bus capacitor is in the discharging stage is continuously judged.

Further, the step of determining whether the dc bus capacitor is in the discharging stage includes:

judging whether the direct current bus capacitor is in a discharging stage by judging whether the direct current bus voltage is in a descending stage, wherein the direct current bus capacitor is in the discharging stage in the descending stage, otherwise, the direct current bus capacitor is not in the discharging stage;

or judging whether the voltage change rate of the direct current bus is smaller than zero to judge whether the direct current bus capacitor is in the discharging stage, if the voltage change rate of the direct current bus is smaller than zero, the direct current bus capacitor is in the discharging stage, otherwise, the direct current bus capacitor is not in the discharging stage.

Further, the step of reconstructing the dc bus current according to the three-phase voltage and the three-phase current at the output side of the inverter includes:

obtaining the corresponding relation between the direct current bus current and the three-phase current at the output side of the inverter;

and obtaining the switching state of a bridge arm of the inverter according to the three-phase voltage at the output side of the inverter.

Further, the direct current bus current at the discharge stage of the direct current bus capacitor is reconstructed by adopting the following expression:

I_ck＝S_a·i_a+S_b·i_b+S_c·i_c+

wherein i_a、i_b、i_cFor three-phase current at the output side of the inverter, I_dcRepresenting the reconstructed DC bus current, S_a、S_b、S_cA, B, C, wherein the corresponding switch state is 1 when the upper arm is turned on and 0 when the lower arm is turned on.

On the other hand, the embodiment of the invention also provides a direct current bus capacitance estimation device, wherein the direct current bus is a direct current bus connected with the input end of the inverter, the capacitance is the capacitance between the direct current buses, and the output end of the inverter is used for driving the motor; the device comprises:

the signal acquisition device is used for measuring the direct-current bus voltage and the three-phase current of the output side of the inverter under the normal working state of the motor;

and the controller is used for reconstructing the direct current bus current according to the three-phase voltage and the three-phase current at the output side of the inverter, and is also used for estimating the capacitance value of the direct current bus by adopting a recursive least square method based on the direct current bus voltage and the reconstructed direct current bus current.

Further, the step of estimating the capacitance value of the dc bus by using a recursive least square method based on the dc bus voltage and the dc bus current obtained by reconstruction specifically uses the following formula to estimate:

C(n)＝C(n-1)+k(n)(n)

wherein, C (n) represents the estimated direct current bus capacitance value of the nth sampling point, n is more than or equal to 1, k (n) represents a gain coefficient, and (n) represents an estimation error;

the formula for k (n) is:

wherein, p (n) represents the middle coefficient of the nth sampling point, x (n) represents the change rate of the dc bus voltage value measured by the nth sampling point, and the calculation formula of p (n) is: p (n) ═ P (n-1) -k (n) x (n) P (n-1),

the formula for x (n) is:v_DC(n) represents the direct current bus voltage value measured by the nth sampling point, and t represents time;

the calculation formula of (n) is: (n) ═ y (n) -C (n-1) x (n),

wherein y (n) represents the reconstructed direct current bus current value measured by the nth sampling point, and the calculation formula of y (n) is as follows: y (n) ═ i_DC(n)。

Further, the direct current bus current at the discharge stage of the direct current bus capacitor is reconstructed by adopting the following expression:

I_dc＝S_a·i_a+S_b·i_b+S_c·i_c+

wherein i_a、i_b、i_cFor three-phase current at the output side of the inverter, I_dcRepresenting the reconstructed DC bus current, S_a、S_b、S_cA, B, C, wherein the corresponding switch state is 1 when the upper arm is turned on and 0 when the lower arm is turned on.

The invention relates to a direct current bus capacitance estimation method and a device based on an AC/DC/AC inverter driving system, which select the measurement data of a discharge area to reconstruct the current of a direct current bus under the normal working condition, is simple and reliable, does not introduce extra voltage and current signals under the normal working state of a motor because the measurement data does not generate interference to the normal operation of the motor, utilizes the characteristic of the charge-discharge process of the direct current bus capacitance, estimates the capacitance value of the direct current bus in the discharge area of the direct current bus capacitance, namely the process of independently supplying power to a load, takes the magnitude of the capacitance value as the evaluation basis of the health condition of the direct current bus capacitance, more effectively explains the state of the direct current bus capacitance, ensures the safe and reliable operation of the inverter system, and optimizes each estimation by adopting a recursive least square method, the final estimation result is more accurate than the average value of each point after estimation, and the sampling frequency and the operation amount are reduced simultaneously, so that the method is more suitable for practical application.

(III) advantageous effects

The technical scheme of the invention has the following beneficial technical effects:

the invention has low requirement on the precision of a voltage and current sensor for collecting data, does not need to access excessive external equipment, can realize the capacitance estimation of the direct current bus only by a controller module with proper precision, has simple principle, high reliability and easy operation, simultaneously abandons the system intrusive operation of high-frequency signal injection, can carry out online real-time estimation on the capacitance of the direct current bus by a simple and easily obtained electric signal, achieves the aim of improving the estimation precision due to the adoption of the recursive least square method, estimates the capacitance of the direct current bus under the condition of not influencing the stable and normal operation of a motor system, and is more suitable for the beneficial effect of industrial application.

Drawings

FIG. 1 is a diagram of an apparatus for estimating capacitance of a DC bus according to an embodiment of the present invention;

FIG. 2 is a basic waveform diagram of the DC bus capacitor voltage according to an embodiment of the present invention;

FIG. 3 is a diagram illustrating a sector distribution of SVPWM voltage vectors according to an embodiment of the present invention;

fig. 4 is a diagram illustrating a correspondence between phase currents under the first sector and dc bus currents according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.

As shown in fig. 1, fig. 1 is a general structural diagram of an estimation device for estimating dc bus capacitance, wherein a motor driving circuit is connected to a motor M, and the motor driving circuit adopts a conventional circuit structure and mainly consists of a three-phase ac power supply e_as、e_bs、e_csThe direct current bus capacitor is connected with a rectifying circuit through a filter circuit L, the rectifying circuit is connected with an inverter circuit, the output end of the inverter circuit is connected with a motor, and a direct current bus capacitor is arranged on a direct current bus between the rectifying circuit and the inverter circuit.

The direct current bus capacitance estimation device comprises a signal acquisition device, a signal processing device and a controller, wherein the signal acquisition device is preferably a high-precision voltage and current probe, and can also be a current sensor, a voltage sensor and the like, and is used for acquiringThe DC bus current reconstruction module in the controller is used for reconstructing DC bus current to obtain a DC bus current signal I_dcSignal processing means for reconstructing the obtained DC bus current signal I_dcAnd the direct current bus voltage signal V acquired by the signal acquisition device_dcThe method comprises the steps of processing signals, wherein a direct current bus capacitance estimation module in a controller is used for estimating a direct current bus capacitance value, preferably, a recursive least square method is used for estimating the direct current bus capacitance value, and further, an evaluation module is provided according to the embodiment of the invention and used for evaluating the health condition of the capacitor according to the direct current bus capacitance value.

The principle of reconstruction of the dc bus current in the present invention is described below with reference to fig. 2-4.

Firstly, the action time period of the reconstruction process of the direct current bus current is introduced, namely the selection of the reconstruction time period.

The result obtained by reconstructing the direct current bus current in the invention is actually the current i_invThat is, the direct current output from the direct current bus side to the inverter side, it is necessary to select the direct current bus current i when selecting the reconstruction region of the direct current bus current_dc＝i_invSuch an operating state. While it is necessary to provide a stable power supply to the load side in order to maintain stable operation of the motor, when the capacitor is charged, the power supply simultaneously charges the capacitor and supplies power to the load. Therefore, the dc bus current in the charging area needs to be considered in addition to the three-phase current on the input side, which is complicated. The discharge phase, discharge region, or discharge state refers to a process in which the capacitor alone supplies power to the load without the source side participating, when i_dc＝i_invAnd discharge zone current i_invThe method can be completely synthesized by three-phase currents on the output side, so that the reconstructed direct-current bus current can completely correspond to the real direct-current bus capacitance current. The invention reconstructs the current of the direct current bus in the selective discharge stage to simply and accurately reconstruct the current of the direct current bus.

Further, the discharge stage is determined by determining whether the dc bus voltage is decreased.

Further, the discharging stage is determined by whether the rate of change of the dc bus voltage is less than zero.

Fig. 2 is a basic waveform diagram of the dc bus capacitor voltage, wherein T1 represents the charging process of the dc bus capacitor, during which the dc bus voltage increases; t2 represents the discharge process of the dc bus capacitance, during which the dc bus voltage drops. In the reconstruction process, only the capacitance state of the T2 part, namely the discharge process of the DC bus capacitance is analyzed, and the DC bus capacitance is analyzed and estimated through the falling process of the capacitance voltage.

As shown in fig. 3, in the conventional SVPWM algorithm, a total of 8 vectors including two zero vectors (V0, V7), i.e., V0-V7, and T1 and T2 correspond to fig. 4, because the inverter control adopts a seven-segment control method, for a voltage vector at a certain time, the zero vector and two of the six non-zero vectors shown in the above figure are synthesized, so T1 and T2 represent the action time of the two non-zero vectors, and Vr is the voltage vector at the time.

Next, as shown in fig. 4, the correspondence between the phase current and the dc bus current in the first sector is displayed, and 3 bridge arm states, that is, switching states, are respectively marked, where the switching state when the upper bridge arm is turned on is defined as 1, the switching state when the lower bridge arm is turned on is defined as 0, and 8 switching states of the inverter correspond to 8 voltage vectors in fig. 3; the first three lines in fig. 4 represent the A, B, C three-phase switch state, the switch state being 1 when the upper arm is on, the switch state being 0 when the lower arm is on, and the fourth line i_dcRepresenting the condition of the direct current bus current, the switch sequence and the direct current bus current have definite corresponding relation, and the current is reconstructed according to the corresponding relation. In fig. 4, in one SVPWM period, a voltage vector V1 acts in a time period T1, at this time, the a-phase upper arm switch is turned on, and the B, C-phase lower arm switch is turned on. The DC bus current is the same as the inverter A phase forward current, i.e. i_a＝i_dcThe voltage vector V2 acts during the period T2, and at this time,A. and the B-phase upper bridge arm switch is conducted, and the C-phase lower bridge arm switch is conducted. The DC bus current is the same as the reverse current of the inverter C, i.e. i_dc＝-i_C. This is also true for the other sectors, and the correspondence between the phase currents of phase a, phase B, and phase C and the dc bus current in all six sectors can be obtained as shown in table 1 below.

TABLE 1

Id1 is a dc bus current when the dc bus current is equal to a phase current of the three-phase currents, and Id2 is a dc bus current when the dc bus current is opposite to the phase current of the three-phase currents. As shown in FIG. 4, the time, i, of the first period of the DC bus being non-zero_dcAnd i_aThe same is the direct current bus current when the direct current bus current is equal to a certain phase current in the three-phase current, and the time when the second section of the direct current bus is not zero, i_dcAnd-i_CAnd the phase current is equal to the phase current in the three-phase current. In short, when the capacitor discharge stage is selected, the current of the direct current bus is related to a certain phase current every moment, and two situations exist, namely the current is equal to the certain phase current or the opposite number of the certain phase current.

According to the corresponding relation, the direct current bus current can be reconstructed under the SVPWM algorithm.

According to the corresponding relation between the three-phase current and the direct current bus current, the following conditions can be known:

I_dc＝S_a·i_a+S_b·i_b+S_c·i_c+

in the above formula, i_a、i_b、i_cFor three-phase current, i, at the output side of the inverter_dcRepresenting the reconstructed DC bus current, S_a、S_b、S_cA, B, C, wherein the corresponding switch state is 1 when the upper arm is turned on and 0 when the lower arm is turned on.

Three-phase switch state S_a、S_b、S_cRepresenting the distribution of each phase current in time sequence, the invention uses the time sequence to process three-phase current i_a、i_b、i_cAnd selecting to obtain the direct current bus current at the discharge stage of the direct current bus capacitor.

The steps for reconstructing the current of the direct current bus are as follows:

and measuring the voltage of the direct current bus, the three-phase voltage and the three-phase current of the output side of the inverter.

And estimating the capacitance value of the direct current bus by adopting a recursive least square method based on the voltage of the direct current bus and the direct current bus current obtained by reconstruction.

The three-phase voltage signal at the output side of the inverter is used as the judgment of the switching state, namely the three-phase switching state S is obtained according to the three-phase voltage signal at the output side of the inverter_a、S_b、S_c1,0 state, when the three-phase voltage signal is non-zero, the switch state of the corresponding phase is 1; when the three-phase voltage signal is zero, the switching state of the corresponding phase is 0. By measuring the three-phase voltage of the output side of the inverter, an additional switch state signal detection device is not required to be introduced, and additional measurement equipment is not required to be added.

The recursive least square method is one of the self-adaptive filters, and utilizes the filter parameters obtained at the previous moment and automatically adjusts the parameters at the current moment according to the estimation error so as to minimize the target function and realize the optimal filtering, the recursive least square method is utilized to realize the accurate estimation of the capacitance value, and the obtained iterative calculation formula of the capacitance value is as follows:the following is a specific estimation procedure:

in the invention, the nominal value C (0) of the capacitor is taken as a first reference value and then substituted into a capacitor voltage formula, namelyCalculating corresponding current value, and reconstructing the calculated current value and the measured current value i of the nth sampling point to obtain the direct current bus current value i_DC(n) comparing, multiplying the obtained calculation error by the gain coefficient to obtain a capacitance estimated value, namely a first capacitance estimated value C (1), taking the capacitance estimated value as a next reference value for cycle iteration until the set operation time or the number of sampling points, updating the gain coefficient according to the current error condition in the cycle iteration process, wherein if the error is small, the gain is larger, and otherwise, the gain is smaller.

The advantage of least squares is that each estimate is optimized and the final estimate must be more accurate than the average of each point estimate.

When the above iterative calculation formula is input into the controller for calculation, the following formula is specifically adopted for expression:

C(n)＝C(n-1)+k(n)(n)

wherein, C (n) represents the estimated direct current bus capacitance value of the nth sampling point, n is more than or equal to 1, k (n) represents a gain coefficient, and (n) represents an estimation error;

the formula for k (n) is:

wherein, p (n) represents the middle coefficient of the nth sampling point, x (n) represents the change rate of the dc bus voltage value measured by the nth sampling point, and the calculation formula of p (n) is: p (n) ═ P (n-1) -k (n) x (n) P (n-1), and x (n) are calculated by the following formula:v_DC(n) represents the direct current bus voltage value measured by the nth sampling point, and t represents time;

the calculation formula of (n) is: (n) ═ y (n) -C (n-1) x (n),

wherein y (n) represents the reconstructed direct current bus current value measured by the nth sampling point, and the calculation formula of y (n) is as follows: y (n) ═ i_DC(n)。

The initial value C (0) is the nominal value of the capacitor, which is the initial value of the capacitance marked on the capacitive element. P (n) represents the intermediate coefficient at the nth iteration, because the nominal value given at the beginning is already relatively close to the true value and it cannot be determined how large the error is, therefore P (n) is set to be small to avoid the deviation of the capacitance estimation result, and preferably P (0) is 0.00001.

And finally, evaluating the health condition of the capacitor according to the capacitance value of the direct current bus.

It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modification, equivalent replacement, improvement and the like made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundaries of the appended claims or the equivalents of such scope and boundaries.