On-line rapid estimation method and device for true RMS (root mean square) of output voltage of inverter

Abstract

The invention discloses an inverter output voltage true virtual value online rapid estimation method and device, and the method comprises the steps: calculating a target output voltage Us according to a dq axis target voltage # imgabs0 # according to a calculation formula: # imgabs1 # calculates a true virtual value Urms of the output voltage according to a real-time DC bus voltage value Udc and the calculated target output voltage Us, the method does not depend on a complex sampling circuit, the true virtual value of the output voltage of the inverter can be estimated in real time through the real-time direct-current bus voltage and the target output voltage which can be obtained in real time, and quick response calculation of the true virtual value of the output voltage of the inverter is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter control, and in particular to a method and device for online rapid estimation of the true effective value of an inverter output voltage. Background Art

[0002] Measuring the effective value of AC voltage is a common task in electric drive experiments and signal detection and analysis. For regular voltage signals (such as sinusoidal waves), the effective value can be calculated based on parameters such as peak-to-peak value and average value, according to their definitions. However, with the advancement of power electronics technology, pulse width modulation (PWM) technology has become widely used in AC outputs, resulting in AC voltages that are not regular sinusoidal. For example, an inverter applies a pulse width modulated voltage signal to the stator windings of a motor. Measuring the effective value of such signals is difficult, yet the effective value of AC voltage is a crucial parameter for describing the motor's electrical power and controlling its normal operation.

[0003] It should be noted that the peak-to-peak or average calculation method utilizes the conversion relationship between the peak value, the rectified average value, and the RMS value of a sine wave. Therefore, these methods are only suitable for measuring the RMS value of sinusoidal signals. For non-sinusoidal signals, the measured "RMS value" is inaccurate. To distinguish this RMS value from the RMS value obtained strictly according to the definition of RMS, the latter is also called true RMS.

[0004] Currently, the main methods for measuring the true RMS value of such irregular AC signals include thermocouple measurement, electronic RMS / DC calculation measurement, and digital discrete synchronous sampling measurement. These methods all require additional hardware for output voltage sampling, measurement, or conversion, which increases the cost of the inverter. For example:

[0005] Patent CN201010610256.6 discloses a method for digitally measuring the output voltage of an inverter, comprising the following steps: sampling the output voltage signal from the inverter output, providing a harmonic filter circuit to filter harmonics; providing a rectifier circuit to rectify the harmonically filtered voltage signal; providing a smoothing filter circuit to smooth and filter the rectified voltage signal to obtain a stable voltage signal; providing a true RMS circuit to perform computational processing on the stable voltage signal; and providing a dedicated A / D chip to sample and convert the processed signal into a digital signal, which is then output to a digital display device via a single-chip microcomputer for display. This method, which samples the output voltage, filters it, rectifies it, and filters it, then uses the true RMS circuit and A / D chip to sample and convert the voltage signal into a digital signal. However, this method suffers from numerous hardware circuits, as well as measurement lag and slow response due to the filtering.

[0006] Patent CN202310292369.3 A fast response calculation method for an AC digital instrument still uses the true effective value calculation method. The sampling period is the same, but the final sampling point is positioned at the current moment. Because of the fixed sampling period, the number of sampling points is the same. For example, N points are sampled in 1 period. If the sampling point at the current moment is used as the final point N, the N-1 points recorded before are used together for calculation. In this way, the current changes can be reflected quickly, and the accuracy is also guaranteed. The sampling point of the instrument at the current moment is the final point of the sampling period, and the sampling period remains unchanged. In this way, the effective value calculation must be performed for each sampling. By calculating in this way, a quick response to changes can be made. This method can achieve fast response calculation of the true effective value, but this method still needs to rely on the voltage sampling circuit to be implemented.

[0007] Therefore, in order to obtain the true effective value of voltage, a method that does not increase hardware cost and can realize online rapid estimation of the true effective value of output voltage is urgently needed. Summary of the Invention

[0008] In the first aspect, the present invention aims to provide a method for online rapid estimation of the true effective value of the output voltage without adding additional hardware costs. The technical solution is as follows:

[0009] A method for quickly estimating the true effective value of an inverter output voltage online includes:

[0010] According to the dq axis target voltage Calculate the target output voltage U s , the calculation formula is:

[0011] According to the real-time DC bus voltage value U dc , and the calculated target output voltage U s , calculate the true effective value of the output voltage U rms , the calculation formula is:

[0012] Furthermore, the dq axis target voltage The method to obtain is:

[0013] According to the target speed n * And the actual motor speed n, use the speed loop PI controller to get the q-axis target current

[0014] Sample the three-phase current I output from the inverter to the motor a , I b , I c , after Clark transformation and Park transformation, the corresponding dq axis actual current I is obtained d, I q ;

[0015] According to the dq axis target current and the actual dq axis current I d , I q , use the current loop PI controller to get the dq axis target voltage in

[0016] Furthermore, the actual motor speed n is obtained by converting the motor rotor position θ obtained by a position sensor into an angle-speed conversion.

[0017] Furthermore, the real-time DC bus capacitor voltage U dc Obtained through adc sampling.

[0018] Furthermore, the method further comprises: Perform inverse Park transform to obtain the corresponding αβ axis target voltage Then, according to the αβ axis target voltage And the real-time DC bus capacitor voltage U obtained by ADC sampling dc , six-way PWM is obtained through the SVPWM calculation module, and the inverter is controlled to output three-phase power to drive the three-phase motor to run at the target speed, thereby realizing the dual closed-loop vector control of the inverter.

[0019] Secondly, the present invention aims to provide a device that can achieve online rapid estimation of the true effective value of the output voltage without adding additional hardware costs. The technical solution is as follows:

[0020] An online rapid estimation device for the true effective value of an inverter output voltage, comprising:

[0021] The first calculation module: according to the dq axis target voltage Calculate the target output voltage U s , the calculation formula is:

[0022] The second calculation module: according to the real-time DC bus voltage value U dc , and the calculated target output voltage U s , calculate the true effective value of the output voltage U rms , the calculation formula is:

[0023] Furthermore, the device further comprises:

[0024] Speed ​​loop PI controller: According to the target speed n * And the actual motor speed n, get the q-axis target current

[0025] Clark converter and Park converter: Convert the three-phase current I from the inverter output to the motor a , I b , I c , after Clark transformation and Park transformation, the corresponding dq axis actual current I is obtained d , I q ;

[0026] Current loop PI controller: according to the dq axis target current and the actual dq axis current I d , I q , get the dq axis target voltage in

[0027] Furthermore, the device further comprises: an angle-speed converter for obtaining the actual speed n of the motor according to the motor rotor position θ.

[0028] Furthermore, the device further comprises: an ADC module, wherein the real-time DC bus capacitor voltage U dc Obtained through adc sampling.

[0029] Furthermore, the device further comprises:

[0030] Inverse Park converter: dq axis target voltage Perform inverse Park transform to obtain the corresponding αβ axis target voltage

[0031] SVPWM calculation module: according to the αβ axis target voltage And the real-time DC bus capacitor voltage U obtained by ADC sampling dc , obtain six-way PWM, and control the inverter to invert and output three-phase power to drive the three-phase motor to run at the target speed.

[0032] Compared with the prior art, the present invention has the following notable features:

[0033] The present invention does not rely on complex sampling circuits and can estimate the true effective value of the inverter output voltage in real time through the real-time DC bus voltage and target output voltage that can be obtained in real time, thereby achieving rapid response calculation of the true effective value. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a block diagram of the inverter control system of the present invention;

[0035] Figure 2 This is the logic block diagram of the output voltage true RMS value estimation module;

[0036] Figure 3 This is a schematic diagram of PWM modulation;

[0037] Figure 4 It is a schematic diagram of the voltage components of the αβ axis;

[0038] Figure 5 It is a schematic diagram of the local PWM waveform of the output voltage. DETAILED DESCRIPTION

[0039] To further illustrate various embodiments, the present invention is provided with accompanying drawings. These drawings form part of the present disclosure and are primarily used to illustrate the embodiments and, in conjunction with the relevant description in the specification, to explain the operating principles of the embodiments. By referring to these drawings, one of ordinary skill in the art will understand other possible embodiments and the advantages of the present invention. The components in the figures are not drawn to scale, and similar reference numerals are generally used to represent similar components.

[0040] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0041] like Figure 1 As shown, the inverter consists of hardware and control system (software algorithm). The hardware is responsible for converting the DC power supply into three-phase AC power according to the six-way PWM control, and at the same time collecting the DC bus capacitor voltage U in real time. dc and three-phase current I a , I b , I c The control system is responsible for the target speed n * , obtain the motor rotor position θ and three-phase current I through the position sensor a , I b , I c and DC bus capacitor voltage U dc Six PWM signals are obtained through software algorithm calculation.

[0042] like Figure 1 As shown in the figure, the inverter control system includes: angle speed converter, speed loop PI controller, Clark converter, Park converter, current loop PI controller, inverse Park converter and SVPWM calculation module, etc., which are used to complete the double closed loop vector control of the inverter. In particular, the output voltage true RMS value estimation module is designed in the control system to estimate the true RMS value of the voltage output by the inverter to the motor. The output voltage true RMS value estimation module uses the target output voltage U s , DC bus voltage U dc And the output voltage true RMS value U rms The numerical relationship between the three is shown in Formula 1.

[0043]

[0044] The inverter control system implements an online fast estimation method for the true RMS value of the inverter output voltage, which includes the following steps:

[0045] Step 1: Use the speed loop PI controller to control the motor speed.

[0046] According to the target speed n * And the actual motor speed n, use the speed loop PI controller to get the q-axis target current The actual motor speed n is obtained by converting the motor rotor position angle θ obtained by the position sensor into an angle-speed conversion.

[0047] Step 2: Use coordinate axis transformation to obtain the current under the dq rotating coordinate axis.

[0048] Sample the three-phase current I output from the inverter to the motor a , I b , I c , after Clark transformation and Park transformation, the corresponding dq axis actual current I is obtained d , I q .

[0049] Step 3: Use the current loop PI controller to control the motor current.

[0050] According to the dq axis target current and the actual dq axis current I d , I q , use the current loop PI controller to get the dq axis target voltage in

[0051] Step 4: Use the output voltage true effective value estimation module to realize online estimation of the inverter output voltage true effective value.

[0052] like Figure 2 As shown, according to the dq axis target voltage And the real-time DC bus capacitor voltage U obtained by ADC sampling dc , the output voltage true RMS value U is obtained through the output voltage true RMS value estimation module rms The specific implementation is:

[0053] First, according to the dq axis target voltage Use formula 2 to calculate the target output voltage U s , where Formula 2 is as follows:

[0054]

[0055] Secondly, according to the real-time DC bus voltage value U dc , and the calculated target output voltage U s , use formula 1 to calculate the true effective value of the output voltage U rms .

[0056] The double closed-loop vector control process of the inverter also includes: the inverter control system controls the dq axis target voltage Perform inverse Park transform to obtain the corresponding αβ axis target voltage Then, according to the αβ axis target voltage And the real-time DC bus capacitor voltage U obtained by ADC sampling dc , six-way PWM is obtained through the SVPWM calculation module, and the inverter is controlled to invert and output three-phase power to drive the three-phase motor to run at the target speed.

[0057] It should be noted that Formula 1 is the target output voltage U under ① sinusoidal PWM modulation and ② dual closed-loop vector control. s And the output line voltage RMS U lr The numerical relationship of ③ output line voltage effective value U lr and the calibration mean value U mn The numerical relationship, and ④ the true RMS value U rms and the calibration mean value U mn The numerical relationship of the actual control output line voltage RMS value U can be obtained by deducing step by step. lr Equal to the calibrated average value U measured by the power analyzer mn , and the DC bus voltage U dc , output line voltage effective value U lr , calibration average value U mn And the output voltage true RMS value U rms The numerical relationship between them is shown in Formula 3.

[0058]

[0059] Formula 3 can finally be simplified to Formula 1.

[0060] The specific derivation process is as follows:

[0061] ①PWM modulation

[0062] PWM, or pulse width modulation, is a technique that simulates a continuous analog signal by varying the width of a series of fixed-frequency pulses, thereby adjusting their duty cycle. In particular, SVPWM, or space vector pulse width modulation, utilizes the switching of the inverter's space voltage vector to produce a circular rotating magnetic field. As a specialized PWM control algorithm, it also exhibits the aforementioned characteristics.

[0063] For example, the inverter control needs to output a peak value of The output voltage at the angle θ is a sinusoidal voltage waveform. Continuously adjusting the duty cycle within a cycle can output the corresponding sinusoidal voltage waveform equivalently, such as Figure 3 shown.

[0064] ② Relationship between the effective value of the target output voltage Us and the output line voltage Ulr under dual closed-loop vector control

[0065] The inverter uses double closed-loop vector control to obtain the target output voltage U s , after transformation, the corresponding αβ axis target voltage is obtained The SVPWM control outputs a three-phase sinusoidal voltage with a fixed voltage amplitude and a fixed frequency, thereby generating a circular rotating magnetic field to drive the motor to run at a fixed speed under a certain load.

[0066] The target output voltage of the inverter is U s 、αβ axis target voltage The schematic diagram of the motor rotor position angle θ is as follows Figure 4 As shown, its numerical relationship satisfies Formula 4.

[0067]

[0068] The equivalent three-phase AC sinusoidal voltage output by the inverter after SVPWM control is consistent with the αβ axis target voltage. The numerical relationship between them is:

[0069]

[0070] The output line voltage expression is shown in Formula 6.

[0071]

[0072] From formula 6, we can see that since the output line voltage is still equivalent to a sine wave, the output line voltage effective value U lr Peak times, that is:

[0073]

[0074] It should be noted that both the output phase voltage and the line voltage exist in the form of PWM modulation waves.

[0075] ③Output line voltage effective value U lr and the rectified average value U calibrated to the effective value mn The numerical relationship of

[0076] Here we need to explain the rectified average value U in the power analyzer that is calibrated to the effective value. mn The definition of rectifier is: The voltage is rectified, the average value is obtained, and then multiplied by a coefficient that becomes the effective value when the input signal is a sine wave; however, if the input waveform is a distorted waveform or a DC waveform, the coefficient will be different from the effective value.

[0077] Rectified average value U calibrated to the effective value mn As shown in Equation 8, with adjustments:

[0078]

[0079] The known approximate calculation formula for the definite integral is shown in Formula 9, which discretizes the definite integral to approximate equivalence, and can be equivalent when n is infinite.

[0080]

[0081] Refer to the definite integral calculation formula. When the sampling frequency of the power analyzer is high, that is, n is large, the discretized expression in Formula 7 can be converted into a definite integral form:

[0082]

[0083] That is equivalent to finding the area enclosed by the voltage curve in the region [0,π].

[0084] refer to Figure 3 As can be seen from the figure, although the output line voltage is in PWM form, it can be equivalent to a sine wave. Based on the above output line voltage amplitude, the corresponding line voltage waveform expression can be expressed as Equation 11.

[0085]

[0086] Substituting the line voltage expression into Equation 9 yields:

[0087]

[0088] From formula 12, we can know that the actual control output line voltage effective value U lrEqual to the rectified average value U measured by the power analyzer and calibrated to the effective value mn .

[0089] ④True effective value U rms and the rectified average value U calibrated to the effective value mn The numerical relationship of

[0090] In the power analyzer's output voltage test, the main observation is the true effective value U rms , quoting the definition in the power analyzer specification: square each instantaneous value, calculate their average, and then take the square root. The calculation formula is shown in Formula 13.

[0091]

[0092] Since the line voltage output by the three-phase PWM control is in PWM form, the following Figure 5 The part of PWM waveform shown in the figure is used to calculate the true effective value U according to the above formula. rms , as shown in Formula 14.

[0093]

[0094] We can further dc Proposed and transformed into:

[0095]

[0096] Similarly, Figure 5 The PWM waveform in the calculation is calibrated to the rectified average value U mn , as shown in Formula 16.

[0097]

[0098] Formula 16 can be transformed into:

[0099]

[0100] Substituting Equation 17 into Equation 15, we can obtain:

[0101]

[0102] Formula 18 expresses the target output voltage U of the inverter. s , DC bus voltage U dc , rectified average value U calibrated to the effective value mn and true RMS value U rms The numerical relationship between them can be finally simplified as shown in Formula 1.

[0103] It should be noted that the calibration mean value U mnCan be measured by power analyzer. Calibrated average value U mn Affected by waveform distortion, the true RMS value U rms The estimated value and true effective value U rms There will be some errors between the measured values.

[0104] At a fixed DC bus voltage U dc Compare different target output voltages U s Output voltage true RMS value U rms The measured and estimated values ​​are shown in Table 1, where the maximum estimated error is 0.4%. The error is within the acceptable range. s After that, the true effective value of the output voltage U can be calculated by formula 1 rms .

[0105] Table 1 True RMS value of output voltage at fixed DC bus voltage U rms Comparison of measured and estimated values

[0106]

[0107] In summary, compared with the prior art, the present invention has the following significant features:

[0108] The present invention does not rely on complex sampling circuits and can estimate the true effective value of the inverter output voltage in real time through the real-time DC bus voltage and target output voltage that can be obtained in real time, thereby achieving rapid response calculation of the true effective value.

[0109] Although the present invention has been particularly shown and described in conjunction with preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made to the present invention without departing from the spirit and scope of the invention as defined in the appended claims, and all such changes are within the scope of protection of the present invention.

Claims

1. A method for online rapid estimation of the true effective value of an inverter output voltage, characterized in that: include: According to the dq axis target voltage Calculate the target output voltage U s , the calculation formula is: According to the real-time DC bus voltage value U dc , and the calculated target output voltage U s , calculate the true effective value of the output voltage U rms , the calculation formula is:

2. The method according to claim 1, wherein The dq axis target voltage The method to obtain is: According to the target speed n * And the actual motor speed n, use the speed loop PI controller to get the q-axis target current Sample the three-phase current I output from the inverter to the motor a , I b , I c , after Clark transformation and Park transformation, the corresponding dq axis actual current I is obtained d , I q ; According to the dq axis target current and the actual dq axis current I d , I q , use the current loop PI controller to get the dq axis target voltage in 3. The method according to claim 2, wherein The actual motor speed n is obtained by converting the motor rotor position θ obtained by a position sensor into an angle-speed conversion.

4. The method according to claim 1, wherein The real-time DC bus capacitor voltage U dc Obtained through adc sampling.

5. The method according to claim 1, wherein Also includes: Target voltage for dq axis Perform inverse Park transform to obtain the corresponding αβ axis target voltage Then, according to the αβ axis target voltage And the real-time DC bus capacitor voltage U obtained by ADC sampling dc , six-way PWM is obtained through the SVPWM calculation module, and the inverter is controlled to output three-phase power to drive the three-phase motor to run at the target speed, thereby realizing the dual closed-loop vector control of the inverter.

6. An online rapid estimation device for the true effective value of an inverter output voltage, characterized in that: include: The first calculation module: according to the dq axis target voltage Calculate the target output voltage U s , the calculation formula is: The second calculation module: according to the real-time DC bus voltage value U dc , and the calculated target output voltage U s , calculate the true effective value of the output voltage U rms , the calculation formula is:

7. The device according to claim 6, characterized in that Also includes: Speed ​​loop PI controller: According to the target speed n * And the actual motor speed n, get the q-axis target current Clark converter and Park converter: Convert the three-phase current I from the inverter output to the motor a , I b , I c , after Clark transformation and Park transformation, the corresponding dq axis actual current I is obtained d , I q ; Current loop PI controller: according to the dq axis target current and the actual dq axis current I d , I q , get the dq axis target voltage Among them I d * =0.

8. The device according to claim 6, wherein Also includes: The angle-speed converter obtains the actual motor speed n according to the motor rotor position θ.

9. The device according to claim 6, wherein Also includes: ADC module, the real-time DC bus capacitor voltage U dc Obtained through adc sampling.

10. The device according to claim 6, wherein Also includes: Inverse Park converter: dq axis target voltage Perform inverse Park transform to obtain the corresponding αβ axis target voltage SVPWM calculation module: according to the αβ axis target voltage And the real-time DC bus capacitor voltage U obtained by ADC sampling dc , obtain six-way PWM, and control the inverter to invert and output three-phase power to drive the three-phase motor to run at the target speed.

Images