Single-phase PWM rectifier direct current side boost type active filter circuit control method based on duty ratio feed-forward single current loop

Abstract

A single-phase PWM rectifier direct-current side boost type active filter circuit control method based on a duty ratio feed-forward single current loop is characterized by comprising the following steps that inductive current of an active filter circuit is collected; collecting the direct current side current of the single-phase PWM rectifier; the method comprises the following steps: extracting a DC side current secondary pulsation component of a PWM rectifier as a reference current of an active filter circuit, performing high-pass filtering on the acquired inductive current of the active filter circuit to filter out a DC component, then subtracting the reference current, and enabling a deviation value to pass through a controller to obtain a current loop control component; the control component per unit of the current loop is added with the voltage control duty ratio Dv of the support capacitor of the active filter circuit for modulation to obtain a control signal of a corresponding switch tube. According to the method, a support capacitor voltage sampling circuit and a control loop of a traditional boost active filter circuit are omitted, the system hardware cost is reduced, the reliability is improved, and the control loop is simplified. The method is suitable for all active filter control which adopts a boost type active filter circuit for filtering on the direct current side, and applicable systems comprise single-phase rectification, single-phase inversion, multi-phase rectification, multi-phase inverters and the like.

Description

Technical Field

[0001] The present invention relates to a control method for a boost-type active filter circuit on the DC side of a single-phase PWM rectifier based on duty cycle feedforward single current loop. Specifically, for a system using an active filter circuit on the DC side of an AC-DC converter or a DC-AC converter, a single current loop control method is adopted for the boost-type active filter circuit, canceling the voltage sensor and voltage loop in the traditional control scheme. Compared with the existing voltage-current double loop control, this control method has the advantages of low hardware cost, high reliability, and simple control structure. Background Art

[0002] Quadrant pulse rectifiers are widely used in various fields due to their characteristics of unity power factor on the grid side, stable DC side voltage, and bidirectional energy flow, such as in power traction drive systems, mine hoist drive systems, and other fields. Due to the inherent characteristics of the AC-DC conversion itself, DC pulsations of corresponding frequencies will be generated on the DC side. For example, in a single-phase AC-DC converter, a second harmonic ripple voltage will appear on the DC side, and a second harmonic ripple current will be generated when flowing through the load; in a three-phase converter, a sixth harmonic ripple voltage will appear on the DC side, and a sixth harmonic ripple current will be generated when flowing through the load. Moreover, if the even-order voltage ripple on the DC output side is not processed, it will be introduced into the control system and odd-order current ripples will be generated on the input side. At the same time, the odd-order current ripples on the input side will also cause the generation of even-order voltage ripples on the output side. Therefore, there are problems of DC side voltage fluctuations and AC side current distortion. When the AC side current distortion is too large, it will seriously affect the power quality of the power grid, resulting in power quality problems such as harmonic pollution and voltage fluctuations. Using LC to filter the second harmonic pulsation on the DC side of single-phase PWM has problems such as large volume, small power density, and poor filtering effect due to parameter drift. Therefore, scholars have studied a compensation method for the second harmonic voltage pulsation based on a boost-type active filter circuit. This method uses an active filter circuit to extract the second harmonic ripple current from the main circuit, reducing the second harmonic ripple current on the output side of the main circuit and thus reducing the second harmonic ripple voltage of the main circuit. This circuit generally uses a nested structure of voltage outer loop and current inner loop for control, where the voltage outer loop ensures that the support capacitor voltage of the active filter circuit works within a reasonable range, and the current inner loop ensures the tracking effect of harmonic current. Its current control signal is composed of a periodic AC signal superimposed with a DC component. Using a traditional PI controller or PR controller alone cannot track the DC component and AC component well at the same time. To solve this problem, the inventor of the present application has applied for a control method for the DC side active filter circuit of a single-phase PWM rectifier using a parallel voltage-current double loop. The designed control system is different from the traditional nested structure of voltage outer loop and voltage inner loop, but uses a parallel structure of voltage loop and current loop, effectively improving the performance of the control system. On this basis, the inventor of the present application further proposes a control method for the boost-type active filter circuit on the DC side of a single-phase PWM rectifier based on duty cycle feedforward single current loop. This method further eliminates the voltage sensor and voltage loop, reducing the system cost, simplifying the control link, and improving the reliability of the system. Summary of the Invention

[0003] The present invention provides a control method for a boost-type active filter circuit on the DC side of a single-phase PWM rectifier based on duty cycle feedforward single current loop.

[0004] A control method for a boost-type active filter circuit on the DC side of a single-phase PWM rectifier based on duty cycle feedforward single current loop, characterized by comprising the following steps:

[0005] A. Collect the inductor current of the active filter circuit; collect the DC-side current of the single-phase PWM rectifier;

[0006] B. Extract the second-order pulsating component of the DC-side current of the PWM rectifier as the reference current of the active filter circuit. Perform high-pass filtering on the collected inductor current of the active filter circuit to filter out the DC component, then subtract it from the reference current, and obtain the current-loop control component after passing the deviation value through the controller;

[0007] C. Normalize the control component of the current loop and add it to the duty cycle D of the support capacitor voltage control of the active filter circuit v and then perform modulation to obtain the control signals of the corresponding switching tubes.

[0008] A control method for a boost-type active filter circuit on the DC side of a single-phase PWM rectifier based on duty-cycle feedforward single current loop, characterized in that the voltage value V of the support capacitor of the active filter circuit cf is determined by D v . Given the DC voltage V of the PWM rectifier dc , the duty cycle D of the support capacitor voltage control of the active filter circuit v can be obtained by the following formula:

[0009]

[0010] A control method for a boost-type active filter circuit on the DC side of a single-phase PWM rectifier based on duty-cycle feedforward single current loop, characterized in that the duty cycle D of the support capacitor voltage control of the active filter circuit v , its upper limit D v_max is determined by the maximum support capacitor voltage V when the active filter circuit operates normally cf_max , and its lower limit D v_min is determined by the minimum support capacitor voltage V when the active filter circuit operates normally cf_min .

[0011] A control method for a boost-type active filter circuit on the DC side of a single-phase PWM rectifier based on duty-cycle feedforward single current loop, characterized in that the duty cycle D of the support capacitor voltage control of the active filter circuit v can be adjusted in real time according to the operating conditions of the active filter circuit, that is, when the load is large, a larger D v is selected; when the load is small, a smaller D v is selected. By dynamically adjusting D v , the loss of the active filter circuit can be reduced.

[0012] This method is applicable to the control of all active filters that use a boost-type active filter circuit for filtering on the DC side. The applicable systems include single-phase rectification, single-phase inversion, polyphase rectification, and polyphase inverters, etc.

[0013] The beneficial effects of the present invention are as follows: This method eliminates the support capacitor sensor and the control loop of the traditional boost-type active filter circuit, reducing the system hardware cost and simplifying the control loop. Description of the Drawings

[0014] Figure 1 It is the circuit topology diagram of a single-phase PWM rectifier using a boost-type active filter circuit.

[0015] u s is the power supply voltage of the single-phase PWM rectifier, i s is the line-side inductor current, R is the equivalent resistance of the inductor, S1 - S6 are the switching tubes of the circuit, C is the support capacitor of the rectifier, i c is the capacitor current, i load is the load current, V dc is the total output voltage of the rectifier, u ab is the input voltage of the single-phase PWM rectifier. This voltage is convenient for analyzing the loop structure of the system and does not need to be collected in actual control. i shc is the secondary ripple current extracted from the rectifier, i shcc is the inductor current of the active filter circuit collected, L f is the inductor parameter of the active filter circuit, C f is the capacitor parameter of the active filter circuit, R f is the equivalent resistance of the inductor of the active filter circuit. To ensure the normal operation of the active filter circuit, it is necessary to make the voltage u cf of the support capacitor of the active filter circuit greater than the DC-side voltage V dc of the rectifier.

[0016] Figure 2 It is the control block diagram of the voltage outer loop and current inner loop of the existing boost-type active filter circuit.

[0017] The steps of the traditional control method are as follows: Subtract the rated voltage u cf from the voltage u cf * of the support capacitor of the active filter circuit to obtain the voltage error signal. Obtain the corresponding current signal through the voltage loop controller, and superimpose the secondary ripple current i shc extracted from the DC side of the single-phase PWM rectifier on this signal to obtain the command current i shcc * of the current controller. Subtract the collected inductor current signal from the command current signal to obtain the current error signal, and then generate a control signal through the current regulator, which is modulated to generate a drive signal.

[0018] Figure 3It is the control block diagram of the parallel voltage loop and current loop control of the Buck / Boost active filter circuit proposed by the inventor in another patent.

[0019] In this control block diagram, the output signal of the voltage loop is no longer input into the current loop controller, but directly generates the corresponding control signal; at the same time, the current sampled by the active filter is filtered and then compared with the reference signal of the current loop. The result generates a control signal through the current controller, and is superimposed with the signal of the voltage loop and then modulated to generate a drive signal.

[0020] Figure 4 It is the control block diagram of the DC-side boost-type active filter circuit of a single-phase PWM rectifier based on duty cycle feedforward single current loop proposed by the present invention.

[0021] In this control method, the voltage sensor and voltage control loop of the active filter are cancelled, and a feedforward voltage duty cycle D is directly given. v This duty cycle signal is superimposed with the signal of the current loop and then modulated to generate a drive signal. Specific implementation mode

[0022] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0023] When using a Boost-type active filter circuit, the voltage V of its support capacitor C f needs to be always higher than the output voltage V of the DC side of the main circuit. cf Therefore, the minimum duty cycle D must be calculated dc to ensure that the active filter circuit can work properly and maintain the required voltage level. v_min When the average value of the energy storage capacitor voltage is constant, the voltage ripple of the energy storage capacitor is proportional to the power output by the system. To meet the working conditions of the active filter circuit, it is necessary to ensure that the minimum value of the energy storage capacitor voltage is higher than the output voltage of the rectifier. In the case of heavy load, the voltage fluctuation range of the energy storage capacitor is the largest. In the case of light load, the ripple of the energy storage capacitor is relatively small, and the difference between it and the output voltage of the rectifier is large. Excessive voltage difference will lead to increased loss, so the voltage difference between the two should be reduced as much as possible.

[0024] Let T be the fluctuation period of the secondary pulsating voltage, V

[0025] and V cf_max represent the maximum and minimum values of the energy storage capacitor voltage respectively, V cf_min represents the average value of the energy storage capacitor, and △V cf_ave represents the peak-to-peak value of the energy storage capacitor. Assume that the output capacitor voltage V of the rectifier cf is constant, and the effective values of the AC voltage and current on the grid side are U dc and I respectively. rms 、Irms , the included angle between the grid-side voltage and current is The grid voltage angular frequency is ωt. At this time, the double-frequency power is mainly reflected in the double-frequency current. Let the double-frequency compensation current be i shcc be:

[0026]

[0027] Then within the time interval [t0, t0 + T / 4], the energy storage capacitor C f is charged, and the capacitor voltage V cf rises. The energy ΔE stored during this period cf is:

[0028]

[0029] It can be seen from Equation (2) that the energy stored in the capacitor is proportional to the power. The energy stored during this period can also be regarded as the difference in the energy storage of the storage capacitor, ΔE cf can also be expressed as:

[0030]

[0031] Relating the two different expressions of ΔE cf together, we can obtain:

[0032]

[0033] Assuming that the average voltage of the energy storage capacitor is the arithmetic mean of the maximum voltage and the minimum voltage, we can get:

[0034]

[0035] Substituting the average value of the energy storage capacitor voltage ΔV cf_ave into ΔV cf we can obtain:

[0036]

[0037] It can be seen from Equation (6) that after the grid angular frequency and the output capacitor of the active filter are determined, when the system operates in a stable state, the average value of the energy storage capacitor is constant, and the pulsation value of the energy storage voltage is proportional to the power of the rectifier. When the power increases, the pulsation of the energy storage voltage also increases. To meet the normal operating conditions of the system, the minimum value of the energy storage capacitor needs to be greater than the rectifier output voltage value, and we can get:

[0038]

[0039] Since the Boost boost type active filter circuit is mainly in the boost operating condition during operation, the volt-second balance relationship can be obtained:

[0040]

[0041] Eliminating the output voltage V of the rectifier by combining equations (6) and (7) dc , the corresponding relationship between the duty cycle, the average value of the energy storage capacitor, and the peak-to-peak value of the energy storage capacitor can be obtained:

[0042]

[0043] Also, because:

[0044]

[0045] Substituting equation (10) into equation (9) gives:

[0046]

[0047] When the rectifier operates at unity power factor and the DC-side load resistance is R L , according to power conservation, we can obtain:

[0048]

[0049] Substituting equation (12) into (11) gives:

[0050]

[0051] Simplifying this expression gives the duty cycle D v and the relationship with the load resistance R L as:

[0052]

[0053] When taking the rated load, the amplitude of the secondary ripple voltage fluctuation is the largest, and at this time, the corresponding equivalent load resistance is the smallest. Let the value on the right side of the equation be A:

[0054]

[0055] Then equation (14) is equivalent to:

[0056]

[0057] where A > 0. From equation (16), the value range of the duty cycle D v can be obtained as:

[0058]

[0059] From this equation, it can be seen that the value on the right side of the inequality is greater than 1, while the duty cycle D vObviously, it cannot be greater than 1. Therefore, the right-side value is discarded, and the minimum boost voltage of the duty cycle D can be obtained. Thus, the voltage loop of the energy storage capacitor is cancelled, and the voltage loop is simplified to the feed-forward duty cycle D, completing the control of the energy storage capacitor voltage.

[0060] Considering the voltage drop V of the switching device diode , the Boost volt-second balance equation can be changed to:

[0061]

[0062] After substituting the above corrected equation, a more accurate derivation result of the minimum duty cycle D v can be obtained. It should be particularly noted that the above derivation assumes that the output voltage of the rectifier is very stable and there is no interference from the secondary ripple voltage, that is, all secondary ripple currents pass through the active filter circuit. However, in actual circuits, this assumption is usually difficult to fully hold, and there will inevitably be a small secondary ripple voltage in the output voltage of the rectifier. Therefore, to ensure the stable operation of the active filter circuit, the minimum duty cycle D v needs to be appropriately increased with a margin. In addition, the dead time of the hardware switching device and the limited switching interval of the duty cycle also need to be considered, that is, the finally determined duty cycle D v should be greater than the calculated minimum duty cycle D v_min to effectively avoid the influence of the secondary ripple voltage of the main circuit and the hardware settings of the switching device on the active filter circuit.

[0063] A control method for a boost-type active filter circuit on the DC side of a single-phase PWM rectifier based on duty cycle feed-forward single current loop, characterized by comprising the following steps:

[0064] A. Collect the inductor current of the active filter circuit; collect the DC side current of the single-phase PWM rectifier;

[0065] B. Extract the secondary pulsating component of the DC side current of the PWM rectifier as the reference current of the active filter circuit, perform high-pass filtering on the collected inductor current of the active filter circuit to filter out the DC component, then subtract it from the reference current, and obtain the current loop control component after passing the deviation value through the controller;

[0066] C. Normalize the control component of the current loop and add it to the duty cycle D v for controlling the voltage of the support capacitor of the active filter circuit, and then perform modulation to obtain the control signal of the corresponding switching device.

[0067] A control method for a boost-type active filter circuit on the DC side of a single-phase PWM rectifier based on duty cycle feed-forward single current loop, characterized in that the voltage value V cf of the support capacitor of the active filter circuit is determined by D v , and in the case of known DC voltage V of the PWM rectifierdc The duty cycle D is controlled by the voltage of the support capacitor of the active filter circuit v which can be obtained by the following formula

[0068]

[0069] A control method for the boost-type active filter circuit on the DC side of a single-phase PWM rectifier based on duty-cycle feedforward single current loop, characterized in that the duty cycle D is controlled by the voltage of the support capacitor of the active filter circuit v whose upper limit D v_max is determined by the maximum support capacitor voltage V when the active filter circuit operates normally cf_max and whose lower limit D v_min is determined by the minimum support capacitor voltage V when the active filter circuit operates normally cf_min

[0070] A control method for the boost-type active filter circuit on the DC side of a single-phase PWM rectifier based on duty-cycle feedforward single current loop, characterized in that the duty cycle D is controlled by the voltage of the support capacitor of the active filter circuit v which can be adjusted in real time according to the operating conditions of the active filter circuit, that is, when the load is large, a larger D is selected v ; when the load is small, a smaller D is selected v . By dynamically adjusting D v the loss of the active filter circuit can be reduced

[0071] This method is applicable to the control of all active filters that use a boost-type active filter circuit for filtering on the DC side. The applicable systems include single-phase rectification, single-phase inversion, polyphase rectification, and polyphase inverters, etc. Compared with the voltage-current series double-loop control of the traditional Boost boost-type active filter, this method not only improves the control effect of the entire system, but also further eliminates the voltage sensor and its control loop of the active filter circuit, reduces the system hardware cost, improves the reliability, and simplifies the control loop​

Claims

1. A control method for a DC-side boost-type active filtering circuit of a single-phase PWM rectifier based on duty cycle feedforward single current loop, characterized in that, Including the following steps: A. Collect the inductor current of the active filter circuit; collect the DC-side current of the single-phase PWM rectifier; B. Extract the second-order pulsating component of the DC-side current of the PWM rectifier as the reference current of the active filter circuit, perform high-pass filtering on the collected inductor current of the active filter circuit to filter out the DC component, then subtract it from the reference current, and obtain the current-loop control component after passing the deviation value through the controller; C. After normalizing the control component of the current loop, add it to the duty cycle D of the active filter circuit to control the voltage of the support capacitor, and then perform modulation to obtain the control signal of the corresponding switching tube. v After adding them together, perform modulation to obtain the control signal of the corresponding switching tube.

2. A control method for a DC-side boost-type active filtering circuit of a single-phase PWM rectifier based on duty cycle feedforward single current loop, characterized in that, The voltage value V of the support capacitor of the active filter circuit cf is determined by D v Given the DC voltage V of the PWM rectifier dc , the duty cycle D for controlling the voltage of the support capacitor of the active filter circuit v can be obtained from the following formula:

3. A control method for a DC-side boost-type active filter circuit of a single-phase PWM rectifier based on duty cycle feedforward single current loop, characterized in that, The duty cycle D is controlled by the voltage of the support capacitor of the active filter circuit v , and its upper limit D v_max is determined by the maximum support capacitor voltage V when the active filter circuit operates normally cf_max , and its lower limit D v_min is determined by the minimum support capacitor voltage V when the active filter circuit operates normally cf_min .

4. A control method for a DC-side boost-type active filter circuit of a single-phase PWM rectifier based on duty cycle feedforward single current loop, characterized in that, The duty cycle D is controlled by the voltage of the support capacitor of the active filter circuit v It can be adjusted in real time according to the operating conditions of the active filter circuit. That is, when the load is large, a larger D is selected v ; when the load is small, a smaller D is selected v . By dynamically adjusting D v , the loss of the active filter circuit can be reduced.

5. This method is applicable to all controls that use a boost-type active filter circuit for filtering on the DC side. The applicable systems include single-phase rectification, single-phase inversion, polyphase rectification, and polyphase inverters, etc.

Images