A power conversion unit direct current side capacitor on-line detection method based on signal extraction method

Abstract

The application discloses a kind of power conversion unit DC side capacitor on-line detection method based on signal extraction method.For with the increase of running time, capacitor gradually ages, the decrease of capacitor capacitance can increase the ripple of submodule capacitor voltage, cause the corresponding increase of device voltage stress and loss, possibly endanger the reliable operation of system.The application does not increase additional hardware circuit, by controlling to make capacitor completely absorb specific harmonic current component to increase the corresponding times harmonic component of capacitor voltage, and combining with adding capacitor voltage regulation module to keep capacitor voltage stable and other harmonic suppression module to realize the suppression to other harmonic, finally, through the measurement of capacitor voltage and on-line estimation calculation, the on-line detection of capacitor capacitance is realized, and the application can accurately and effectively monitor and evaluate the health status of capacitor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronic converter, and particularly relates to a power conversion unit DC side capacitor online detection method based on signal extraction method. BACKGROUND

[0002] In the power conversion unit, the capacitor is one of the key components prone to failure. With the running time, the capacitor will gradually age, which is specifically manifested as the decrease of the capacitance value and the increase of the equivalent series resistance (ESR). The decrease of the capacitance value will lead to the increase of the sub-module capacitor voltage ripple, thereby increasing the device voltage stress and the power conversion unit loss. The increase of the ESR will lead to the increase of the capacitor loss, thereby causing the temperature to rise and further accelerating the capacitor aging. When the capacitor aging reaches the failure threshold, the aging speed will sharply increase. At this time, the system can still run, but the negative influence caused by the capacitor aging will endanger the reliability of the system. The capacitor aging detection is usually to detect the capacitance value. The conventional solution can record the increment of the capacitor voltage and the corresponding charging time at the system startup, and estimate the capacitance value by using the RC charging curve of the capacitor. The method is simple and easy to implement, but cannot realize the real-time monitoring of the health status of the sub-module. SUMMARY

[0003] The purpose of the present application is to provide a power conversion unit DC side capacitor online detection method based on signal extraction method, which can realize the online detection of the capacitance value with high precision by only measuring the bus capacitor voltage without additional hardware circuit.

[0004] The present application provides a power conversion unit DC side capacitor online detection method based on signal extraction method, the main circuit of which comprises an AC power grid input, a front-stage AC / DC converter, a bus capacitor, a rear-stage DC / DC converter and a DC load output. The input side of the front-stage AC / DC converter is connected with the AC power grid, the bus capacitor is connected in parallel between the AC / DC converter and the DC / DC converter, and the output side of the rear-stage DC / DC converter is connected with the DC load. The method of the present application does not increase additional hardware circuit, and controls the input power to only include the second harmonic component and the fourth harmonic component except the fundamental component by controlling the front-stage AC / DC converter control module, and controls the rear-stage DC / DC converter control module to suppress the fourth harmonic component of the bus capacitor voltage and the second harmonic component of the current flowing into the rear-stage DC / DC converter, so that the second harmonic component of the input power is completely absorbed by the bus capacitor, and the fundamental component and the fourth harmonic component are transmitted to the DC / DC converter. The second harmonic component of the input power can be obtained by measuring the input voltage and current, and the generated voltage ripple is only related to the capacitance value of the bus capacitor. Therefore, the current capacitance value of the bus capacitor can be calculated by measuring the capacitor voltage, thereby realizing the online detection of the capacitance value.

[0005] The control system of the entire circuit includes a front-end AC / DC converter controller and a back-end DC / DC converter controller. For the front-end AC / DC converter controller, according to a specific embodiment of the present invention, it may include a line-phase voltage conversion module, a PLL phase-locked loop module, a third harmonic injection module, a feedforward module, an output voltage control module, an input current control module, and an SPWM modulation module; sampling the three-phase grid input line voltage v. AB v BC v CA It is converted into phase voltage V through a line-to-phase voltage conversion module. AN v BN v CN Each of these modules is then connected to the input terminals of the PLL phase-locked loop module, the third harmonic injection module, and the feedforward module, respectively. The PLL phase-locked loop module outputs the grid voltage phase angle ωt; the third harmonic injection module outputs the adjustment amount m of the third harmonic modulation wave. A (3) ~m C (3) The feedforward module outputs the adjustment amount m of the feedforward modulated wave. A (1) ~m C (1) The output voltage V is sampled by the output voltage control module. o The reference value V is obtained through the PI controller. o-ref Output quantity i d-ref The input current control module samples the three-phase input current i A i B i C Connected to the input terminal of the abc / dq coordinate transformation module, the d-axis component i of the fundamental wave of the input current is obtained after filtering. d and q-axis component i q The reference values ​​for the fundamental currents on the d-axis and q-axis are i d-ref And 0, the PI controller outputs m d and m q The adjustment amount m is output by the dq / abc coordinate transformation module. A (1*) ~m C (1*) ; All adjustment values, i.e., m A (1) ~m C (1) m A (3) ~m C (3) and m A (1*) ~m C (1*) The corresponding sums yield the three-phase modulation wave adjustment amount m. A~m C The switch signal of each switch tube of the pre-stage AC / DC converter is obtained after being modulated by the SPWM modulation module.

[0006] The post-stage DC / DC converter controller comprises a direct-current capacitor voltage regulation module, a current second harmonic suppression module and a voltage fourth harmonic suppression module. Taking the current second harmonic suppression module as an example, the current is delayed by T / 6 and T / 3, and then is structured into three-phase a, b and c, and is outputted by the abc / dq coordinate transformation module with phase θ=2ωt, so that only the second harmonic component is a direct current, the fundamental wave and other harmonic waves are alternating currents, and the current second harmonic component d-axis component i d (2) and the q-axis component i q (2) are obtained by filtering. d (2) The PI controller is used to adjust i q (2) to be zero, and the PI controller output is obtained by the dq / abc coordinate transformation module to obtain the second harmonic compensation frequency f s2 ; the voltage fourth harmonic suppression module has the same idea, the voltage is delayed by T / 12 and T / 6, and then is structured into three-phase a, b and c, and is outputted by the coordinate transformation module with phase θ=4ωt, so that the fourth harmonic component is a direct current, and the fourth harmonic regulation frequency f s4 is obtained. s0 The direct-current component control frequency f s2 outputted by the current second harmonic suppression module and the fourth harmonic compensation frequency f s4 outputted by the voltage fourth harmonic suppression module are added to the initial switching frequency F to obtain the switching frequency f s of the post-stage DC / DC converter, and the switch signal of each switch tube of the post-stage DC / DC converter is obtained by the PFM modulation module.

[0007] The bus capacitor voltage, the input current and the input voltage are sampled, and the capacitor capacity at the measurement moment is calculated by a formula:

[0008]

[0009] Wherein, V ph is the fundamental wave voltage amplitude of the power grid, I ph is the fundamental wave current amplitude of the power grid, k3 is the amplitude coefficient of the injected third harmonic, ω is the working angular frequency of the power grid voltage, v bus-max is the maximum value of the bus capacitor voltage, and V is the direct-current component of the bus capacitor voltage. The capacitor capacity online diagnosis can be realized by comparing the measured capacitor capacity with the reference value.

[0010] Compared with the prior art, the present application has the following beneficial effects:

[0011] By using the control method, the health state of the DC side capacitor of the power conversion unit can be detected in real time with high precision during the working process. The scheme does not need additional circuit, can be applied to different power conversion module topologies, and supports online real-time detection. Meanwhile, only low-frequency capacitor voltage, input voltage and current need to be sampled in the scheme, and the sampling is not easy to be affected by sampling noise, and the sampling is simple, and the capacitor value at the measurement time can be directly calculated. By using closed-loop control, the influence of disturbance on measurement is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 Fig. 1 is a schematic diagram of a power conversion module main circuit;

[0013] Figure 2 Fig. 2 is a schematic diagram of capacitor aging detection and judgment;

[0014] Figure 3 Fig. 3 is a schematic diagram of a power conversion module front-stage AC / DC converter controller;

[0015] Figure 4 Fig. 4 is a schematic diagram of a power conversion module rear-stage DC / DC converter controller according to the present application; DETAILED DESCRIPTION

[0016] The present application will be described in detail below with reference to specific embodiments and drawings. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that the modifications or improvements made without departing from the concept of the present application are within the scope of the present application.

[0017] According to a specific embodiment of the present application, the power conversion unit is composed of two stages, the front-stage AC / DC converter 2 selects CHB converter, the rear-stage DC / DC converter 4 selects LLC converter, and the bus capacitor 3 is connected in parallel between the AC / DC converter 2 and the DC / DC converter 4. The DC side capacitor online diagnosis method of the power conversion unit based on the signal extraction method of the present application includes, without additional circuit, suppressing the fifth and seventh harmonics by the front-stage AC / DC converter 2, injecting the third harmonic to reduce the current stress and make the power flowing into the bus capacitor 3 and the rear-stage DC / DC converter 4 only contain the fundamental component, the second harmonic component and the fourth harmonic component. Suppressing the fourth harmonic component of the bus capacitor 3 voltage and the second harmonic component of the current flowing into the rear-stage DC / DC converter 4 by the rear-stage DC / DC converter 4, so that the input power second harmonic component is completely absorbed by the bus capacitor 3, and the fundamental and fourth harmonic components are all transmitted to the rear-stage DC / DC converter 4. The input power second harmonic component can be obtained by measuring the input voltage and current, and the voltage ripple generated by the absorption of the bus capacitor is related to the capacitance value, so that the input voltage, input current and bus capacitor voltage can be sampled to realize the online diagnosis of the capacitor. Specifically:

[0018] Referring to Figure 1 , the main circuit includes the input AC grid 1, the front-stage AC / DC converter 2, the bus capacitor 3, the rear-stage DC / DC converter 4 and the DC load 7; the AC side of the front-stage AC / DC converter 2 is connected to the AC grid, the bus capacitor 3 is connected in parallel between the AC / DC converter 2 and the DC / DC converter 4, and the output side of the rear-stage DC / DC converter 4 is connected to the DC load 7; the AC / DC converter control module 5 controls the front-stage AC / DC converter 2, and the DC / DC converter control module 6 controls the rear-stage DC / DC converter 4. Among them AB , v BC , v CA are three-phase grid line voltages, i A , i B , i C are three-phase grid currents, v o is the output voltage, all of which are sampled to the front-stage AC / DC converter controller 5 for control, C bus is the DC side bus capacitor, v bus is the DC side bus capacitor voltage, i bus is the current flowing into the rear-stage DC / DC converter 4, wherein v bus and i bus are sampled to the rear-stage DC / DC converter controller 6 for control.

[0019] In the case of injecting the third harmonic, considering the symmetry of three-phase voltage, the three-phase grid phase voltage v AN (t), v BN(t), v CN (t) can be expressed as:

[0020]

[0021] where V ph is the amplitude of the fundamental voltage of the power grid; k3 is the amplitude coefficient of the injected third harmonic; ω is the working angular frequency of the voltage of the power grid.

[0022] The three-phase input current i A (t), i B (t), i C (t) can be expressed as:

[0023]

[0024] where I ph is the amplitude of the fundamental current of the input current.

[0025] Since the high-order power harmonic content is extremely small and can be ignored, the three-phase input power p A (t), p B (t), p C (t) can be calculated as:

[0026]

[0027] Since the three phases have symmetry. Taking the A phase as an example for analysis, the equivalent input power p(t) of the power conversion unit is the A-phase input power:

[0028]

[0029] The front-stage AC / DC converter 2 is composed of four switching tubes, and basically does not consume input power in the working process, so the sum of the power transmitted to the bus capacitor 3 and the rear-stage DC / DC converter 4 is the input power p(t) of the power module. The current second harmonic suppression module 603 and the voltage fourth harmonic suppression module 602 are included in the controller 6 of the rear-stage DC / DC converter, the current second harmonic suppression module 603 suppresses the transmission of the second harmonic power to the DC / DC converter 4, so that the second harmonic power is completely absorbed by the bus capacitor 3, and the voltage fourth harmonic suppression module 602 suppresses the absorption of the fourth harmonic power by the bus capacitor 3, and the capacitor does not absorb the fundamental power in the steady state. Therefore, the power absorbed by the bus capacitor 3 is:

[0030]

[0031] The bus capacitor 3 can be equivalent to an ideal capacitor C bus and a capacitor equivalent resistance ESR in series, and the second ripple power absorbed by the ESR is much smaller than the C busTherefore, the power absorbed by the bus capacitor without considering the ESR can be expressed as the product of voltage and current, that is,

[0032]

[0033] The simultaneous equations are obtained as follows: bus The expression is:

[0034]

[0035] wherein V is the fundamental component of the bus capacitor voltage.

[0036] The peak value of the bus capacitor voltage is obtained by sampling, and taking the maximum value as an example, the maximum value of the bus capacitor voltage is v bus-max The expression is:

[0037]

[0038] Therefore, the bus capacitor value C bus The expression is:

[0039]

[0040] Since k3 is the coefficient given by the third harmonic injection link, and the grid operating frequency ω is known, the current bus capacitor value can be calculated by sampling the bus capacitor voltage, the input grid voltage and the input grid current. The capacitor aging diagnosis is usually diagnosed by detecting the capacitor value, and the health condition of the capacitor can be judged by comparing the calculated value after sampling with the initial value. According to a specific example of the present application, a capacitor aging detection and judgment schematic diagram is shown in Figure 2 .

[0041] According to a specific example of the present application, the control method of the front-stage AC / DC converter 5 shown in Figure 3 is adopted, and the front-stage AC / DC converter controller 5 comprises a line voltage conversion module 501, a PLL phase-locked loop module 502, a third harmonic injection module 503, a feedforward module 504, an output voltage control module 505, an input current control module 506, and an SPWM modulation module 507. The three-phase grid line voltages v AB , v BC , and v CA are sampled, and the three-phase phase voltages v AN , v BN , and v CN, are connected to the input of the PLL module 502, the third harmonic injection module 503 and the feedforward module 504 respectively; the PLL module 502 outputs the phase angle ωt of the grid voltage and is connected to the input of the third harmonic injection module 503, the abc / dq coordinate transformation module and the dq / abc coordinate transformation module; the third harmonic injection module 503 outputs the adjustment amount m of the third harmonic modulation wave with amplitude coefficient k3 A (3) ~m C (3) ; the feedforward module 504 introduces the grid voltage into the control loop to improve the dynamic performance, and outputs the feedforward modulation wave m A (1) ~m C (1) ; the three-phase grid current i A , i B , i C and the output voltage v o are sampled, and the output voltage v o is compared with the reference value V o-ref to output the d-axis reference value i d-ref of the fundamental component of the three-phase grid current through the PI controller. The three-phase grid current i A , i B , i C is transformed into the d-axis and q-axis components i d and i q of the fundamental component through the abc / dq coordinate transformation module and filtering, and the reference values of i d and i q are i d-ref and 0 respectively, and the adjustment amount output by the PI controller is transformed into the adjustment amount m of the input current fundamental modulation wave through the dq / abc coordinate transformation module A (1*) ~m C (1*) . All the modulation wave adjustment amounts are added to obtain the total adjustment amount m A ~m C , which is modulated by the SPWM modulation module 507 to obtain the switching signal of each switch tube of the pre-stage AC / DC converter 2.

[0042] The specific implementation of each module of the pre-stage AC / DC converter controller 5 is as follows:

[0043] The PLL module 502 obtains the phase angle ωt of the grid voltage through a software phase-locked algorithm.

[0044] The feedforward module 504 introduces the grid voltage into the control loop to improve the dynamic performance, and outputs the feedforward modulation wave m A (1) ~m C(1) The ratio of the phase voltage input to the sum of the intermediate bus voltage in each module in the phase.

[0045] The third harmonic injection module 503 is used to inject a given third harmonic m A (3) ~m C (3) The phase voltage v AN , v BN , v CN The abc / dq coordinate transformation module is used to perform dq coordinate transformation according to the grid voltage phase ωt, and the d-axis component i d The phase of the third harmonic is the same as that of the fundamental wave, and the amplitude is the product of the fundamental wave amplitude and the given third harmonic injection coefficient k3.

[0046] The output voltage control module 505 is used to subtract the output voltage sampling from the output voltage reference value V o-ref , and the error value obtained is input into the PI controller to output the fundamental wave d-axis reference value i d-ref .

[0047] The input current control module 506 is used to perform dq coordinate transformation according to the grid voltage phase ωt through the abc / dq coordinate transformation module, and the d-axis and q-axis components i d and i q of the filtered fundamental wave current are obtained. The reference value of i d is i d-ref , and the reference value of i q is 0. The d-axis and q-axis error inputs of the PI controller are obtained by subtracting i A (1*) ~m C (1*) .

[0048] The SPWM modulation module 507 compares the three-phase modulation wave signals m A ~m C obtained by adding with the high-frequency carrier signal, respectively, to obtain square wave pulse signals with a duty cycle that changes with the modulation signal, which are used as the switching signals of the switching tubes of the front-stage AC / DC converter.

[0049] The control method of the rear-stage DC / DC converter 4 shown in FIG. Figure 4 The DC / DC converter control module 6 includes a DC bus capacitor voltage regulation module 601, a voltage fourth harmonic suppression module 602, a current second harmonic suppression module 603, and a PFM modulation module 604. The bus capacitor C bus voltage v bus, the difference between the reference value V bus-ref and the sampling value v s0 is input into the PI controller to obtain the fundamental wave compensation amount f bus of the switching frequency of the post-stage LLC converter. bus The current second harmonic suppression module 603 and the voltage fourth harmonic suppression module 602 are respectively used to suppress the second harmonic of the current flowing into the post-stage LLC converter and the fourth harmonic of the bus capacitor voltage, and the current i bus flowing into the post-stage LLC converter and the bus capacitor voltage v s2 are sampled to obtain the second harmonic compensation amount f s4 and the fourth harmonic compensation amount f s0 of the switching frequency of the post-stage LLC converter through the current second harmonic suppression module 603 and the voltage fourth harmonic suppression module 602 respectively. s2 The sum of f s4 , f s and the rated switching frequency F of the LLC converter is added to obtain the switching frequency f bus of the post-stage LLC converter, and after the PFM modulation module 604, the switching signal of the switching tube of the post-stage LLC converter is obtained.

[0050] The specific implementation of the post-stage DC / DC converter control module 6 is as follows:

[0051] The capacitor voltage regulation module 601 is used to control the voltage V bus-ref across the bus capacitor to be stable, and the capacitor voltage reference value V bus is subtracted from the sampling value v s0 of the bus capacitor voltage to obtain an error value, and the PI controller is used to calculate the fundamental wave compensation amount f bus of the switching frequency of the post-stage LLC converter.

[0052] The current second harmonic suppression module 603 is used to suppress the second harmonic of the current i bus flowing into the post-stage LLC converter, and the sampled current i bus is delayed by T / 6 and T / 3 (T is the power frequency period) respectively, and is input into the abc / dq coordinate transformation with the phase of the three-phase signal being 2ωt. After the dq transformation, the low-pass filter is input, and since the current only has the d-axis component and the q-axis component of the second harmonic as the direct current, the d-axis component and the q-axis component of other harmonics and the fundamental wave are obtained as the alternating current, and the d-axis component i d (2) and the q-axis component i q (2) of the second harmonic current are obtained after the filtering. d (2) The d-axis and q-axis second harmonic current reference values are both 0, and the d-axis component i q (2)Subtracting from 0, the resulting error value is processed by a PI controller, and the result is then transformed into dq / abc coordinates with a phase of 2ωt. After the abc transformation, the second harmonic compensation amount f for the switching frequency of the subsequent LLC converter is obtained. s2 .

[0053] The fourth harmonic voltage suppression module 602 is used to suppress the voltage V flowing into the bus capacitor. bus The fourth harmonic in the sampled current V bus Delay by T / 12 and T / 6 respectively (T is the power frequency period), and compare with current V bus The system constructs an abc / dq coordinate transformation with a 4ωt phase input of a three-phase signal. After the dq transformation, the signal is input to a low-pass filter. Since only the fourth harmonic d-axis and q-axis components of the voltage are DC quantities, while the d-axis and q-axis components of other harmonics and the fundamental frequency are AC quantities, the filter yields the d-axis component i of the fourth harmonic current. d (4) and q-axis component i q (4) The reference values ​​for the fourth harmonic current on both the d-axis and q-axis are set to 0. The d-axis component i... d (4) and q-axis component i q (4) Subtracting from 0, the resulting error value is processed by a PI controller, and the result is transformed into dq / abc coordinates with a phase of 4ωt. After the abc transformation, the fourth harmonic compensation amount f of the switching frequency of the subsequent LLC converter is obtained. s4 .

[0054] LLC converter switching frequency fundamental compensation amount f s0 Second harmonic compensation amount f s2 Fourth harmonic compensation amount f s4 The operating frequency f of the subsequent LLC converter is obtained by superimposing the rated operating frequency FR with the rated operating frequency FR. s The PFM module 604 uses frequency f s The frequency of the square wave pulse signal is changed to serve as the switching signal for the switching transistors of the subsequent LLC converter.

[0055] This invention addresses the problem of increased voltage stress and power module losses in power conversion units due to capacitor aging over time. Without adding additional hardware circuitry, it employs a control mechanism to ensure the capacitor fully absorbs specific harmonic components of the power, thereby increasing the corresponding harmonic components of the capacitor voltage. A capacitor voltage control loop is added to maintain capacitor voltage stability, and a harmonic suppression module suppresses other harmonics. By measuring the capacitor voltage, the capacitance value can be detected online, enabling accurate and effective monitoring and evaluation of the capacitor's health status.

Claims

1. A power conversion unit DC side capacitor online detection method based on signal extraction method, the input side of the front stage AC / DC converter is connected to an AC power grid, a parallel bus capacitor is connected between the front stage AC / DC converter and the rear stage DC / DC converter, and the output side of the rear stage DC / DC converter is connected to a DC load; characterized in that, The method is to control the front-stage AC / DC converter to suppress the fifth and seventh harmonics, inject the third harmonic to reduce the current stress, and make the input power only include the second and fourth harmonic components except the fundamental component, control the power conversion unit rear-stage DC / DC converter by using the rear-stage controller, suppress the bus capacitor voltage harmonic components except the second one, and suppress the second harmonic component of the current flowing into the rear-stage DC / DC converter, so that the double-frequency ripple power is completely absorbed by the bus capacitor, the capacitor capacitance value is calculated by measuring the generated capacitor voltage ripple, and the online detection of the capacitor capacitance value is realized, and the capacitor capacitance value at the measurement moment is: ； Where V ph is the grid fundamental voltage amplitude; I ph is the grid fundamental current amplitude; k3 is the amplitude coefficient of the injected third harmonic; is the grid voltage operating angular frequency; v bus-max is the bus capacitance voltage maximum value, V is the bus capacitance voltage DC component; comparing the measured capacitance value with the reference value can realize online diagnosis of the capacitance value.

2. The method according to claim 1, wherein, The post-stage controller comprises a capacitor voltage regulation module, a current second harmonic suppression module, a voltage fourth harmonic suppression module and a PFM modulation module; the capacitor voltage regulation module samples the voltage v bus of the bus capacitor on the direct current side of the power conversion unit and inputs the difference between the reference value V bus-ref to a PI controller to generate a fundamental wave compensation amount f s0 of the switching frequency of the post-stage DC / DC converter; the current second harmonic suppression module and the voltage fourth harmonic suppression module are respectively used for suppressing the second harmonic component of the current flowing into the post-stage DC / DC converter and the fourth harmonic component of the capacitor voltage on the direct current side of the bus, and the generated modulation signals are respectively the second harmonic compensation amount f s2 and the fourth harmonic compensation amount f s4 of the switching frequency obtained by taking the reference value of the harmonic component as zero; the three compensation amounts f s0 , f s2 and f s4 are superimposed on the initial switching frequency F of the post-stage DC / DC converter to obtain the final switching frequency f s of the post-stage DC / DC converter; and the frequency signal f s is input to the PFM modulation module to obtain the switching signals of the four switching tubes S5-S8 of the post-stage DC / DC converter.

3. The method according to claim 2, wherein, The second harmonic compensation amount f s2 The determination method is as follows: the current is delayed by T / 6 and T / 3, and is configured with abc three-phase, T is the power frequency period, the abc / dq coordinate transformation module with phase θ=2ωt outputs only the second harmonic component as the direct current, the fundamental wave and other harmonic waves are alternating currents, and the current second harmonic component d-axis component i d (2) And q-axis component i q (2) , the PI controller is adjusted to zero through i d (2) And i q (2) , the PI controller output is obtained through the dq / abc coordinate transformation module The second harmonic compensation frequency f s2 ; the voltage fourth harmonic suppression module has the same idea, the voltage is delayed by T / 12 and T / 6, and is configured with abc three-phase, so that the fourth harmonic component is transformed into direct current, the abc / dq coordinate transformation module θ=4ωt, and the fourth harmonic adjustment frequency f s4 is obtained.

Images