阅读说明：本技术 一种永磁同步电机驱动系统最小损耗控制方法 (Minimum loss control method for permanent magnet synchronous motor driving system ) 是由 郝晓红 李明彦 王子琦 于 2019-10-14 设计创作，主要内容包括：本发明涉及一种永磁同步电机驱动系统最小损耗控制方法。永磁同步电机的供电逆变器采用不连续脉冲宽度调制策略。首先分析了一个基波周期内,基于采用DPWM调制策略的供电逆变器的开关工作状况,并定量地计算了供电逆变器损耗。随后研究了供电逆变器输出电流、电压谐波对永磁同步电机损耗的影响,并给出了附加损耗的数值计算公式。在此基础上,建立了永磁同步电机损耗模型,同时将逆变器损耗和供电逆变器输出谐波带来的附加损耗纳入系统损耗计算中,并计算出整个系统损耗最小时的定子电流用于最小损耗控制。最后建立了考虑逆变器损耗以及逆变器谐波带来的损耗的永磁同步电机最小损耗控制框图。(The invention relates to a minimum loss control method for a permanent magnet synchronous motor driving system. A power supply inverter of the permanent magnet synchronous motor adopts a discontinuous pulse width modulation strategy. Firstly, the switching working condition of the power supply inverter based on the DPWM (digital pulse width modulation) strategy in a fundamental wave period is analyzed, and the loss of the power supply inverter is calculated quantitatively. And then, the influence of the output current and voltage harmonic of the power supply inverter on the loss of the permanent magnet synchronous motor is researched, and a numerical calculation formula of the additional loss is given. On the basis, a permanent magnet synchronous motor loss model is established, meanwhile, the loss of the inverter and the additional loss caused by the harmonic wave output by the power supply inverter are brought into the system loss calculation, and the stator current when the loss of the whole system is minimum is calculated and used for minimum loss control. And finally, establishing a minimum loss control block diagram of the permanent magnet synchronous motor considering the loss of the inverter and the loss brought by harmonic waves of the inverter.)

1. A method of minimum loss control for a permanent magnet synchronous motor of a system, the method comprising:

the problem of loss of a power supply inverter in a permanent magnet synchronous motor driving system is considered, a DPWM (digital pulse width modulation) strategy for reducing the loss of the inverter is adopted, and harmonic voltage output by the power supply inverter and additional iron loss and additional copper loss generated by injecting current into the permanent magnet synchronous motor are considered; and finally, establishing a loss model of the permanent magnet synchronous motor during sinusoidal voltage power supply, finally obtaining the total loss of the whole system of the permanent magnet synchronous motor, and solving the stator current which enables the loss of the whole system to be minimum as a given value so as to realize minimum loss control.

2. The control method of claim 1, wherein the problem of loss of the power supply inverter is taken into account when calculating the problem of loss of the permanent magnet synchronous motor, and a DPWM (digital pulse width modulation) strategy is adopted to reduce the loss of the inverter;

and the loss of the power supply inverter adopting the DPWM (digital pulse width modulation) strategy is quantitatively calculated, and the on-state loss is as follows:

in the formula

When the power device of the inverter is switched in a switching period, the switching-on energy loss E of the power device can be generated at least once_onTurn-off energy loss E of power device_offAnd freewheeling diode reverse turn-off loss E_rrTherefore, using the data manual for IGBTs, three-phase switching losses can be approximated as:

wherein N is a carrier ratio; e_on、E_off、E_rrProvided by a data manual;

3. The control method according to claim 1, wherein the loss problem of the permanent magnet synchronous motor is calculated by considering the output harmonic voltage of the power supply inverter, the additional iron loss and the additional copper loss generated by current injection into the permanent magnet synchronous motor;

and the inverter outputs harmonic waves to add loss to the permanent magnet synchronous motor, wherein the additional loss comprises additional iron loss and additional copper loss. The additional iron loss can be deduced on the basis of a Bertotti discrete iron loss calculation model; the additional iron loss can be derived on the basis of a Bertotti discrete iron loss calculation model. According to the Bertotti discrete iron loss settlement model, the iron loss of the motor during sinusoidal power supply is as follows:

in the formula P_irThe iron loss for supplying sine power is hysteresis loss, eddy current loss and abnormal loss. K_hAnd x is the hysteresis loss coefficient; k_e、K_eaRespectively obtaining an eddy current loss coefficient and an abnormal loss coefficient; f is the magnetic field frequency, N is the number of turns of the coil, and S is the sectional area of the iron core; u. of_avIs the average value of voltage u_rmsIs the effective value of the voltage; the hysteresis loss is related to the voltage average value according to the formula; the eddy current loss is related to the effective value of the voltage;

for the inverter adopting DPWM modulation, when the carrier ratio is large enough, the average value of the output voltage and the average value of the fundamental wave voltage can be considered to be equal, so that the hysteresis loss is equal to that of the sine power supply, the abnormal loss and the minimum difference under the standard sine are considered to be small when the inverter supplies power, and the additional iron loss under the power supply of the DPWM-modulated inverter is mainly the increased eddy current loss; from the above equation, the eddy current loss is related to the square of the effective voltage value, so the additional iron loss of the DPWM-modulated inverter power supply is:

in the formula (I), the compound is shown in the specification,

4. The method for calculating the iron loss and the copper loss caused by the harmonic voltage of the inverter output harmonic waves and the current injected into the permanent magnet synchronous motor according to the claim 3; it is characterized in that the additional copper loss can be analyzed by the harmonic component in the current. Let the non-sinusoidal current flowing through the whole conducting bar be i, and express the current as the sum of a series of different sinusoidal alternating currents according to Fourier series, namely the sum of each harmonic current, namely

In the formula I_μ、ω_μ、α_μRespectively is effective value, angular velocity and initial phase angle of mu-order harmonic current phasor;

the impedance experienced by the high frequency harmonics increases due to the current skin effect, so that the total copper loss is equal to

Wherein the content of the first and second substances,

in the formula R_dThe direct current resistance of the whole conducting bar;

the resistance increase coefficient under each harmonic can be solved by a finite element method, so that the copper loss of the motor under the power supply of the inverter is

5. The control method according to claim 1, characterized in that: when the inverter supplies power, the loss of the whole system consists of five parts, namely (1) inverter loss (2) additional copper loss (3) additional iron loss (4) copper loss during standard sinusoidal power supply (5) iron loss during standard sinusoidal power supply; all losses are addedObtaining the total loss P of the driving system of the permanent magnet synchronous motor when the DPWM modulation inverter supplies power_LLet us order

the current loop is positioned at the inner layer of two control loops in the system, the dynamic response speed is fastest, and because the control of the current is realized under a synchronous rotating coordinate system, three-phase current needs to be detected firstly, and d-axis and q-axis currents i are calculated_dAnd i_qTo obtain d and q axis currents i_dAnd i_qThen, i is mixed_dComparing with a reference value of d-axis current of the stator when the loss is minimum obtained by a system loss control module i_qComparing with the current reference value after the outer ring is set, and obtaining the expected voltage U under the synchronous rotating coordinate system by the action of the current regulator on the difference value_d、U_qThen, the U is put_d、U_qVoltage value U converted to three-phase stationary coordinate system_a、U_bAnd U_c. After the DPWM algorithm of zero sequence voltage injection is modulated, a modulation signal is input into an inverter, and the inverter acts on the permanent magnet synchronous motor to complete primary current control.

The speed loop is an outer layer control loop of the system, the speed loop needs to compare a detected speed value with a set value, an expected q-axis current is obtained after a difference value is acted by a speed regulator, in practice, the response speed of the speed loop is lower than that of a current loop, and the control period of the speed loop is generally more than 10 times that of the current loop during design.

Technical Field

The invention relates to a minimum loss control method of a permanent magnet synchronous motor system, belongs to the field of motor control, and simultaneously relates to a discontinuous pulse width modulation strategy of an inverter.

Background

Permanent Magnet Synchronous Motors (PMSM) have been widely used in various fields because of their advantages such as high efficiency, high power density and high power factor. In recent years, as the application of permanent magnet synchronous motors in the industrial field is increasingly widespread, it has become a research hotspot to adopt new materials, improve motor design or further improve motor efficiency through a minimum loss control method. The motor minimum loss control method can be mainly divided into a minimum loss control method based on a model and a minimum loss control method based on a search algorithm.

In the first category, loss model control is based on accurate mathematical description, and the working point corresponding to the minimum motor loss is calculated through complex calculation. But has the defects of large calculation amount and strong dependence on motor parameters.

In the second category, the search technique does not need an accurate function expression, and it is premised on keeping the output power constant, i.e. the motor output torque and the rotating speed are kept constant in a steady state, the d-axis current or the stator flux linkage is continuously adjusted, and the input power is measured at the same time. When the input power is minimum, the system efficiency reaches the optimal point, and the corresponding exciting current is the optimal exciting current. The search technology generally has the defects of slow search and poor convergence.

There are three problems with the minimum loss control of existing permanent magnet synchronous motors: 1. the main body of research is a permanent magnet synchronous motor, and the loss of a power supply inverter is ignored; 2. the centers of gravity of research are all placed on a control method aiming at the motor, and the influence of a modulation strategy of a power supply inverter on the loss of the inverter is ignored; 3. the additional loss of the output time current harmonic of the power supply inverter to the permanent magnet synchronous motor is ignored.

Disclosure of Invention

The invention mainly aims at the problem that the additional loss of the permanent magnet synchronous motor caused by the inverter loss and the inverter output current time harmonic wave is not considered in the traditional minimum loss control of the permanent magnet synchronous motor. A DPWM (digital pulse width modulation) strategy is adopted to replace the traditional SVPWM strategy, and a permanent magnet synchronous motor system minimum loss control strategy considering the additional loss caused by the loss of an inverter and the time current harmonic thereof is provided. The implementation steps are as follows:

step 1: and (3) realizing the DPWM (digital pulse width modulation) strategy and quantitatively calculating the loss of the inverter. The DPWM modulation strategy enables the switching devices to clamp at 1/3 cycles with a switching frequency of 2/3 of the SVPWM modulation strategy, so the DPWM switching loss is equal to 2/3 of the SVPWM switching loss. DPWM is realized by injecting zero-sequence components, injected zero-sequence components are adjusted by detecting phase difference of output voltage and current, current peak value tracking in a clamping interval is realized, and inverter loss minimization is realized. The implementation method is shown in the attached figure 1.

If the line loss is not considered, the main loss of the inverter is composed of two parts: (1) on-state losses in the on-state; (2) switching losses in the turn-on and turn-off processes of the power semiconductor device. The on-state loss is higher in proportion at a lower switching frequency, and conversely, the switching loss is higher in proportion.

And (4) assuming that the three-phase loss of the inverter is the same, establishing an A-phase inverter loss model under DPWM modulation.

The voltage drop V of the two ends of the IGBT is known_ceVoltage drop V across diode_DThe current flowing through the power device is A phase current i_A(n) and the on-time of the device in one switching cycle is

The on-state loss of the inverter in one fundamental period is:

in the formula

f_zFor the switching frequency of the inverter, since the DPWM has 1/3 periods of inactivity in each fundamental wave period, the switching frequency is equal to 2/3 times the carrier frequency, f is the modulated waveThe frequency of the radio frequency is set to be,in order to delay the output current from the phase angle of the output voltage and to achieve the same three-phase switching law, the total on-state loss P_con＝3*P_conA。

The inverter switching power loss expression is: p_SW＝E_SWF, in the formula E_SWIs the switching loss in one modulation period. When the power device of the inverter is switched in a switching period, the switching-on energy loss E of the power device can be generated at least once_onTurn-off energy loss E of power device_offAnd freewheeling diode reverse turn-off loss E_rr. Therefore, by using the data manual of the IGBT, the three-phase switching loss can be approximated as:

wherein N is a carrier ratio; e_on、E_off、E_rrProvided by a data manual;

in order to be the reference bus voltage,

is the reference switch current amplitude; v_DCIs the actual bus voltage, I_SWIs the actual switching current magnitude.

Step 2: and the inverter outputs harmonic waves to add loss to the permanent magnet synchronous motor, wherein the additional loss comprises additional iron loss and additional copper loss. The additional iron loss can be derived on the basis of a Bertotti discrete iron loss calculation model. According to the Bertotti discrete iron loss settlement model, the iron loss of the motor during sinusoidal power supply is as follows:

in the formula P_irThe three parts on the right side of the equation are hysteresis losses respectively for the iron losses of the sine power supplyEddy current losses, abnormal losses. K_hAnd x is the hysteresis loss coefficient; k_e、K_eaRespectively obtaining an eddy current loss coefficient and an abnormal loss coefficient; f is the magnetic field frequency, N is the number of turns of the coil, and S is the sectional area of the iron core; u. of_avIs the average value of voltage u_rmsIs the effective value of the voltage. The hysteresis loss is related to the voltage average value according to the formula; the eddy current loss is related to the effective value of the voltage.

When the inverter supplies power, the fundamental wave of the voltage is u₁(t)＝u_msin ω t, instantaneous voltage value:

for an inverter using DPWM modulation, when the carrier ratio is sufficiently large, the output voltage average value and the fundamental voltage average value thereof can be considered to be equal. The hysteresis loss is therefore equal to that of the sinusoidal supply. The ratio of the output voltage effective value of the inverter modulated by the DPWM to the sinusoidal voltage power supply effective value is as follows:

considering that the phase difference between the abnormal loss and the standard sine is very small when the inverter supplies power, the additional iron loss of the motor under the condition that the inverter supplies power modulated by the DPWM is mainly increased eddy current loss. From the above equation, the eddy current loss is related to the square of the effective voltage value, so the additional iron loss of the DPWM-modulated inverter power supply is:

in the formula (I), the compound is shown in the specification,

for the total harmonic distortion, the contents of the remaining components other than the fundamental wave, i.e., the degree of distortion of the output voltage from the ideal sinusoidal voltage, can be compared.

The additional copper loss can be analyzed by the harmonic content of the current. Let the non-sinusoidal current flowing through the whole conducting bar be i, and express the current as the sum of a series of different sinusoidal alternating currents according to Fourier series, namely the sum of each harmonic current, namely

In the formula I_μ、ω_μ、α_μThe effective value, angular velocity and initial phase angle of the mu-order harmonic current phasor are respectively.

The impedance experienced by the high frequency harmonics increases due to the current skin effect, so that the total copper loss is equal to

Wherein the content of the first and second substances,

representing the loss, R, of the mu-harmonic alone through the whole bar_μIs the ac resistance of the whole conducting bar at the mu harmonic. Obviously, the ac resistance values corresponding to different harmonics are not equal, and to quantitatively describe the resistance value increase degree, the resistance increase coefficient corresponding to the μ harmonic is defined as:

in the formula R_dIs the dc resistance of the entire bar.

The resistance increase coefficient under each harmonic can be solved by a finite element method, so that the copper loss of the motor under the power supply of the inverter is

And step 3: loss model of permanent magnet synchronous motor. The equivalent circuit of the surface-mounted permanent magnet synchronous motor considering iron loss under the rotor magnetic field orientation two-phase rotating coordinate system is shown in the attached figure 2.

In the sine wave power supply, the iron loss of the permanent magnet synchronous motor can be expressed as

In the formula: Ψ_SIs the stator flux linkage amplitude; omega is the rotation electrical angle of the rotor; lambda [ alpha ]_cIs a coefficient related to eddy current loss; lambda [ alpha ]_hIs a coefficient related to hysteresis loss. The copper consumption of the permanent magnet synchronous motor during sine wave power supply can be expressed as

Meanwhile, according to the equivalent circuit, the equivalent circuit can be derived

And 4, step 4: and (4) a system minimum loss control strategy. The loss of the whole system during the inverter power supply is composed of (1) the inverter loss (2) additional copper loss (3) additional iron loss (4) copper loss during the standard sine power supply (5) iron loss during the standard sine power supply (5). When all losses are added to obtain the total loss P of the driving system of the permanent magnet synchronous motor when the DPWM modulation inverter supplies power_L. Order to

The d-axis current torque component of the stator with the minimum loss can be obtained. And the minimum loss control of the permanent magnet synchronous motor system based on the DPWM can be realized by using the calculated d-axis current set value of the stator for motor control. The invention adopts a vector control strategy, adopts two closed-loop PI control to a control system, and sequentially comprises a current loop and a speed loop from an inner layer to an outer layer, wherein each control loop is elaborated as follows:

the current loop is positioned in the inner layer of two control loops in the system, and the dynamic response speed is fastest. Since the current control is performed in a synchronous rotating coordinate system, it is necessary to detect three-phase currents and calculate d and q-axis currents i_dAnd i_q. D and q axis currents i are obtained_dAnd i_qThen, i is mixed_dComparing with a reference value of d-axis current of the stator when the loss is minimum obtained by a system loss control module i_qComparing with the current reference value after the outer ring is set, and obtaining the expected voltage U under the synchronous rotating coordinate system by the action of the current regulator on the difference value_d、U_qThen, the U is put_d、U_qVoltage value U converted to three-phase stationary coordinate system_a、U_bAnd U_c. After the DPWM algorithm of zero sequence voltage injection is modulated, a modulation signal is input into an inverter, and the inverter acts on the permanent magnet synchronous motor to complete primary current control.

The speed loop is an outer layer control loop of the system, the speed loop needs to compare a detected speed value with a set value, an expected q-axis current is obtained after a difference value is acted by a speed regulator, in practice, the response speed of the speed loop is lower than that of a current loop, and the control period of the speed loop is generally more than 10 times that of the current loop during design. Thus, the minimum loss control system is shown in FIG. 3.

Drawings

FIG. 1 is a block diagram of a DPWM implementation by injecting zero-sequence components;

FIG. 2 is an equivalent circuit diagram of a permanent magnet synchronous motor;

FIG. 3 is a minimum loss control block diagram of a PMSM system;

Detailed Description