Rectifier DC side ripple suppression method and system for input voltage drop

Abstract

The present invention provides a method and system for suppressing ripple on the DC side of a rectifier for input voltage drop, and relates to the field of rectifiers. The method comprises: calculating a three-phase input voltage; calculating a three-phase switching function based on the three-phase input voltage; making an overmodulation zone judgment, and when it is determined that the instruction current vector is located in the linear modulation zone, determining an output voltage reference value based on the calculation result of the three-phase switching function, and suppressing the DC side voltage ripple of a three-phase current type PWM rectifier based on the calculation result of the three-phase switching function and the output voltage reference value. The method has the advantages of improving the efficiency of suppressing the ripple on the DC side of the rectifier in the input voltage drop scenario and reducing the control cost.

Description

Technical Field

[0001] The present invention relates to the field of rectifiers, and in particular to a method and system for suppressing ripple on a DC side of a rectifier when input voltage drops. Background Art

[0002] In order to achieve a higher input voltage utilization rate, the three-phase current PWM (Pulse Width Modulation) rectifier in engineering practice often works under a condition with a large modulation index. However, when the three-phase system is faulty due to equipment failure, grounding fault, or the load on one phase far exceeds the load on other phases, the three-phase input voltage will drop severely, increasing the imbalance. At this time, if the three-phase current PWM rectifier still works under a relatively high modulation index, the command current vector may move outside the linear modulation area - the nonlinear modulation area, causing the output voltage of the three-phase current PWM rectifier to have a large even-order ripple. In order to suppress the rectifier from working in the nonlinear modulation area when the input voltage imbalance is large, the present invention proposes a linear modulation area algorithm under the condition of large imbalance, which can suppress the DC side voltage ripple caused by the rectifier working in the nonlinear modulation area when the input voltage drops severely.

[0003] When the input voltage drops severely, the existing control modulation strategy has limited effect on suppressing the voltage ripple on the DC side of the three-phase current-type PWM rectifier. Therefore, a DC / DC converter is usually cascaded on the DC side of the three-phase current-type PWM rectifier to maintain the output voltage stable by controlling the subsequent DC / DC converter. Figure 1 The topology and control block diagram of the existing three-phase current-source PWM rectifier cascade Buck converter shown in some embodiments of this specification are as follows: Figure 1 As shown in the figure, the front-stage three-phase current-source PWM rectifier adopts an unbalanced control strategy, and the control loop of the rear-stage Buck converter consists of an output voltage outer loop and an inductor current inner loop. The sampled output voltage v dc With the output voltage reference After passing through the comparator, it is sent to the PI controller to obtain the inductor current reference value Inductor current reference value The sampled inductor current is sent to the quasi-proportional resonant (QPR) controller through a comparator to obtain the command voltage. Command voltage With the output voltage reference The ratio is the power switch tube Q of the subsequent Buck converter. dWhen the three-phase input voltage drops severely, in order to suppress the voltage pulsation on the DC side, an additional auxiliary circuit needs to be added to the back stage of the three-phase current-type PWM rectifier, which increases the additional cost. Since multiple resonant controllers need to be connected in parallel, the design and debugging of the controller are more complicated.

[0004] Therefore, it is necessary to provide a method and system for suppressing ripple on the DC side of a rectifier for input voltage drop, so as to improve the efficiency of suppressing ripple on the DC side of the rectifier in the input voltage drop scenario and reduce the control cost. Summary of the invention

[0005] The present invention provides a method for suppressing ripple on the DC side of a rectifier for input voltage drop, comprising: calculating a three-phase input voltage; calculating a three-phase switching function based on the three-phase input voltage; making an overmodulation zone judgment, and when it is determined that the instruction current vector is located in a linear modulation zone, determining an output voltage reference value based on a calculation result of the three-phase switching function, and suppressing the DC side voltage ripple of a three-phase current type PWM rectifier based on the calculation result of the three-phase switching function and the output voltage reference value.

[0006] Furthermore, the calculation of the three-phase switching function based on the three-phase input voltage includes: calculating the duty cycle of the effective current vector and the duty cycle of the zero vector based on the three-phase input voltage; calculating the three-phase switching function based on the duty cycle of the effective current vector and the duty cycle of the zero vector.

[0007] Furthermore, when the command current vector is in the linear modulation region, the three-phase switching function is: Among them, v a is the phase A voltage, v b is the voltage of phase B, v c is the C phase voltage, σ is the switching function of the three-phase bridge arm, σ a is the switching function of the bridge arm of phase a, σ b is the switching function of the bridge arm of phase b, σ c is the switching function of the c-phase bridge arm.

[0008] Furthermore, the output voltage reference value is determined based on the calculation result of the three-phase switching function, including: calculating the modulation index based on the target current vector amplitude, the DC side current, the output voltage and the input voltage amplitude; determining the output voltage reference value constraint based on the modulation index; calculating the output voltage reference value based on the calculation result of the three-phase switching function and the output voltage reference value constraint.

[0009] Furthermore, the output voltage reference value is constrained to be: in, is the output voltage reference value, V p is the amplitude of the positive sequence component of the three-phase input voltage, VN is the amplitude of the negative sequence component of the three-phase input voltage.

[0010] Further, the determining the output voltage reference value constraint based on the modulation degree includes: calculating a margin voltage; and determining the output voltage reference value constraint based on the modulation degree and the margin voltage.

[0011] Further, calculating the margin voltage includes: calculating the margin voltage based on the switching loss of the power switch tube and the parasitic resistance of the device.

[0012] Furthermore, the calculation formula of the margin voltage is: Among them, V d is the margin voltage, I dc is the DC side current, r L2 is the parasitic resistance of the output filter inductor, R s is the on-state resistance of the switch tube, is the target current vector value, r L1 is the parasitic resistance of the input filter inductor.

[0013] Furthermore, based on the calculation result of the three-phase switching function and the output voltage reference value, the DC side voltage ripple of the three-phase current-type PWM rectifier is suppressed, including: the sampled output voltage and the output voltage reference value are sent to the first PI controller after passing through a comparator to obtain a current inner loop reference value; the current inner loop reference value and the sampled inductor current are sent to the second PI controller after passing through a comparator to obtain a voltage inner loop output; based on the calculation result of the three-phase switching function and the voltage inner loop output, the DC side voltage ripple of the three-phase current-type PWM rectifier is suppressed.

[0014] The present invention provides a rectifier DC side ripple suppression system for input voltage drop, comprising: a voltage calculation module, used to calculate the three-phase input voltage; a function calculation module, used to calculate the three-phase switching function based on the three-phase input voltage; a suppression control module, used to perform overmodulation area judgment, when it is determined that the instruction current vector is located in the linear modulation area, based on the calculation result of the three-phase switching function, determine the output voltage reference value, based on the calculation result of the three-phase switching function and the output voltage reference value, suppress the DC side voltage ripple of the three-phase current type PWM rectifier.

[0015] Compared with the prior art, the method and system for suppressing ripple on the DC side of a rectifier during input voltage drop provided by the present invention have at least the following beneficial effects:

[0016] When the three-phase input voltage drops, it is only necessary to separate the positive and negative sequence components of the input voltage. By adjusting the output voltage reference value, the even-frequency ripple on the DC side of the rectifier can be suppressed without adding additional hardware and controller costs. Since the output voltage is already a ripple-free DC quantity, a good control effect can be achieved by using a PI controller, which can save hardware and controller costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] This specification will be further described in the form of exemplary embodiments, which will be described in detail by the accompanying drawings. These embodiments are not restrictive, and in these embodiments, the same number represents the same structure, wherein:

[0018] Figure 1 It is a topology and control block diagram of an existing three-phase current-source PWM rectifier cascade Buck converter shown in some embodiments of this specification;

[0019] Figure 2 It is a flow chart of a method for suppressing ripple on the DC side of a rectifier when input voltage drops according to some embodiments of this specification;

[0020] Figure 3 It is a topology and control block diagram of a rectifier DC side ripple suppression method for input voltage drop according to some embodiments of this specification;

[0021] Figure 4 is a schematic diagram of the spatial distribution of positive and negative sequence current vectors in a complex plane when the input is unbalanced according to some embodiments of this specification;

[0022] Figure 5 is a schematic diagram of the running trajectory of the space current vector in the complex plane under the unbalanced control strategy shown in some embodiments of this specification;

[0023] Figure 6a It is a simulated waveform diagram of the DC side output voltage and input current of a three-phase current-type PWM rectifier that is not controlled to the linear modulation region according to some embodiments of this specification;

[0024] Figure 6b It is a simulation waveform diagram of the DC side output voltage and input current of a three-phase current-type PWM rectifier controlled to the linear modulation region according to some embodiments of this specification;

[0025] Figure 7a It is a schematic diagram of simulated waveforms of DC-side output voltage and input current of a three-phase current-type PWM rectifier that is not controlled to a linear modulation region according to some embodiments of this specification;

[0026] Figure 7bIt is a schematic diagram of simulated waveforms of DC-side output voltage and input current of a three-phase current-type PWM rectifier controlled to a linear modulation region according to some embodiments of this specification;

[0027] Figure 8a is a schematic diagram of input and output waveforms using an auxiliary circuit ripple suppression strategy according to some embodiments of this specification;

[0028] Figure 8b is a schematic diagram of input and output waveforms of a linear modulation area control algorithm according to some embodiments of this specification;

[0029] Fig. 9 It is a module schematic diagram of a rectifier DC side ripple suppression system for input voltage drop according to some embodiments of this specification. DETAILED DESCRIPTION

[0030] In order to more clearly illustrate the technical solutions of the embodiments of this specification, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some examples or embodiments of this specification. For ordinary technicians in this field, this specification can also be applied to other similar scenarios based on these drawings without creative work. Unless it is obvious from the language environment or otherwise explained, the same reference numerals in the figures represent the same structure or operation.

[0031] Figure 2 is a flow chart of a method for suppressing ripple on the DC side of a rectifier when input voltage drops according to some embodiments of this specification, such as Figure 2 As shown, the method for suppressing ripple on the DC side of a rectifier for input voltage drop may include the following steps.

[0032] Step 210, calculating the three-phase input voltage.

[0033] Specifically, the three-phase input voltage under unbalanced conditions can be expressed as:

[0034]

[0035] Among them, v an is the A phase input voltage, v bn is the B phase input voltage, v cn is the C phase input voltage, v aP , v bP , v cP Represents the positive sequence component of the three-phase input voltage, v aN , v bN , v cN Represents the negative sequence component of the three-phase input voltage, V PRepresents the amplitude of the positive sequence component of the input voltage, V N Represents the amplitude of the negative sequence component of the input voltage, α p Represents the phase angle of the positive sequence component of the input voltage, α N Represents the phase angle of the negative sequence component of the input voltage.

[0036] Under the unbalanced control strategy, the three-phase input current is controlled to follow the three-phase input voltage, so the three-phase input current can be expressed as:

[0037]

[0038] Among them, i aP ,i bP ,i cP Represents the positive sequence component of the three-phase input current, i aN ,i bN ,i cN Represents the negative sequence component of the three-phase input current, I P Represents the amplitude of the positive sequence component of the input current, I N Represents the amplitude of the negative sequence component of the input current, α p Represents the phase angle of the positive sequence component of the input current, α N Represents the phase angle of the negative sequence component of the input current.

[0039] In the equilibrium state, the space current vector is:

[0040] I=α+jβ=I m [cos(ωt)+jsin(ωt)]

[0041] It can be seen that the current vector in the equilibrium state can be expressed in the complex plane as m The space synchronous rotating vector of. Similarly, the space current vector of the three-phase current type PWM rectifier when the input voltage is unbalanced is:

[0042] I=I P +I N

[0043] in,

[0044]

[0045] When the input voltage is unbalanced, under the unbalanced control strategy, the space current vector can be decomposed into the angular velocity ω and the amplitude I P The positive sequence space current vector I rotating counterclockwise in the complex plane P With angular velocity ω, amplitude I N The negative-sequence space current vector I rotating clockwise in the complex plane N The initial angle of the positive sequence current vector relative to the α axis is φP , the initial angle of the negative sequence current vector relative to the α axis is -φ N The spatial distribution of the positive sequence current vector and the negative sequence current vector in the complex plane is as follows: Figure 4 As shown. Since the positive sequence space current vector I P and the negative sequence space current vector I N The rotation direction in the complex plane is opposite, so from I P , I N The trajectory of the synthetic space current vector I is I P +I N is the long axis, I P -I N is the elliptical trajectory of the minor axis. When the input is unbalanced, the spatial distribution of the positive and negative sequence current vectors in the complex plane is as follows: Figure 4 As shown, when v an =141.2∠0°, v bn =113∠-120°, v cn =141.2∠120°, the running trajectory of the space current vector I in the complex plane under the unbalanced control strategy is as follows: Figure 5 shown.

[0046] Step 220, calculating a three-phase switching function based on the three-phase input voltage.

[0047] Specifically include:

[0048] Based on the three-phase input voltage, the three-phase switching function is calculated, including:

[0049] Based on the three-phase input voltage, the duty cycle of the effective current vector and the duty cycle of the zero vector are calculated;

[0050] Based on the duty cycle of the effective current vector and the duty cycle of the zero vector, the three-phase switching function is calculated.

[0051] Under unbalanced working conditions, when the command current vector moves to sector I, the action time duty ratio of the non-zero current vector and the zero current vector can be expressed as:

[0052]

[0053] Among them, d6, d1 and d0 represent the duty cycle of the action time corresponding to the current vectors I6, I1 and I0 respectively.

[0054] The switching function matrix in sector I can be expressed as:

[0055]

[0056] Then, the expression of the three-phase switching function in sector I can be calculated as follows:

[0057]

[0058] Among them, v a is the phase A voltage, v b is the voltage of phase B, v c is the C phase voltage, σ is the switching function of the three-phase bridge arm, σ a is the switching function of the bridge arm of phase a, σ b is the switching function of the bridge arm of phase b, σ c is the switching function of the c-phase bridge arm.

[0059] When the input voltage is unbalanced, the linear modulation area of ​​the rectifier is deformed into an ellipse. When it is larger, d6+d1>1 exists, and the command current vector will run into the overmodulation area. At this time, the on-time duty cycle can be redistributed. The specific formula is:

[0060]

[0061] Among them, d′6, d′1 and d′0 respectively represent the redistributed current vector I6, and the duty cycle of the action time corresponding to I1 and I0 is.

[0062] The expression of the three-phase switch function after redistribution is calculated as follows:

[0063]

[0064] It can be seen that when the output voltage reference value When is large, the on-time duty cycle of the three-phase bridge arm switch tube can be divided into two cases: (1) the command current vector does not move to the overmodulation area, and (2) the command current vector moves to the overmodulation area.

[0065] When the command current vector does not move to the overmodulation area, the expression of the three-phase switching function of the three-phase current-type PWM rectifier in the entire waveform period is:

[0066]

[0067] When the command current vector moves to the overmodulation area, the three-phase switching function will have different expressions as the target current vector moves to different sectors, as shown in Table 1:

[0068] Table 1

[0069]

[0070]

[0071] Combined with Table 1, it can be seen that when the three-phase input is unbalanced and the three-phase current-source PWM rectifier is over-modulated under the unbalanced control strategy, the output voltage expression is shown in Table 2.

[0072] Table 2

[0073]

[0074]

[0075] The output voltage when overmodulation occurs under unbalanced input voltage is a piecewise function. When the target current vector has not moved to the overmodulation area, the rectifier can accurately synthesize the command current vector. When the target current vector moves to the overmodulation area, the rectifier can only partially synthesize along the direction of the target current vector, and the output voltage cannot reach the voltage reference value.

[0076] In some embodiments, determining the output voltage reference value based on the calculation result of the three-phase switching function includes:

[0077] Calculate the modulation degree based on the target current vector magnitude, the DC side current, the output voltage and the input voltage magnitude;

[0078] Based on the modulation index, determine the output voltage reference value constraint;

[0079] Based on the calculation result of the three-phase switching function and the output voltage reference value constraint, an output voltage reference value is determined.

[0080] Specifically, when the three-phase input voltage is unbalanced, the linear modulation region of the three-phase current-source PWM rectifier under the unbalanced control strategy is I P +I N is the long axis, I P -I N is the elliptical trajectory of the short axis. Since the running trajectory of the target current vector is always a circular trajectory, the target current vector value that always moves in the linear modulation area can be obtained as:

[0081]

[0082] In the formula, I P is the amplitude of the positive sequence component of the three-phase input current, I N is the amplitude of the negative sequence component of the three-phase input current.

[0083] Since the DC side voltage v of the three-phase current-type PWM rectifier dc It can be regarded as the AC side voltage v Cx (x=a,b,c) modulation, so it can be obtained according to the target current vector amplitude I ref , DC side current Idc , output voltage V o With input voltage amplitude V m , determine the modulation index M, The output voltage reference value constraint can be obtained as:

[0084]

[0085] in, is the output voltage reference value, that is, v * dc , V p is the amplitude of the positive sequence component of the three-phase input voltage, V N is the amplitude of the negative sequence component of the three-phase input voltage. When the three-phase input voltage drops severely, it is only necessary to separate the positive and negative sequence components of the input voltage, and the even-frequency ripple on the DC side of the rectifier can be suppressed by adjusting the output voltage reference value; when the target current vector moves in the linear modulation area, the three-phase current-type PWM rectifier can accurately synthesize the target current vector and the output voltage reference value, so the target current vector can always move in the linear modulation area by adjusting the output voltage reference value, avoiding even harmonics in the output voltage due to overmodulation under unbalanced conditions.

[0086] In some embodiments, in order to prevent the over-modulation phenomenon caused by the dynamic adjustment of the controller in the control loop causing the output voltage reference value input to the SVPWM modulation link to be too high, a certain margin should be left when setting the output voltage reference value. Therefore, based on the modulation index, the output voltage reference value constraint is determined, including:

[0087] Calculate the margin voltage;

[0088] Based on the modulation degree and the margin voltage, an output voltage reference value constraint is determined.

[0089] For example, the margin voltage may be calculated based on the switching loss of the power switch tube and the parasitic resistance of the device.

[0090] As an example only, the margin voltage is calculated as:

[0091]

[0092] Among them, V d is the margin voltage, I dc is the DC side current, r L2 is the parasitic resistance of the output filter inductor, R s is the on-state resistance of the switch tube, is the target current vector value, r L1 is the parasitic resistance of the input filter inductor.

[0093] Step 230, perform overmodulation area judgment. When it is determined that the command current vector is located in the linear modulation area, determine the output voltage reference value based on the calculation result of the three-phase switching function. Based on the calculation result of the three-phase switching function and the output voltage reference value, suppress the DC side voltage ripple of the three-phase current type PWM rectifier.

[0094] Figure 3 is a topology and control block diagram of a rectifier DC side ripple suppression method for input voltage drop according to some embodiments of this specification, such as Figure 3 As shown, specifically including:

[0095] The sampled output voltage and the output voltage reference value are sent to the first PI controller after passing through a comparator to obtain a current inner loop reference value;

[0096] The current inner loop reference value and the sampled inductor current are sent to the second PI controller through a comparator to obtain the voltage inner loop output;

[0097] Based on the calculation results of the three-phase switching function and the voltage inner loop output, the DC side voltage ripple of the three-phase current-source PWM rectifier is suppressed.

[0098] Figure 3 In, v dc Indicates the output voltage, v o * Represents the output voltage reference value, v * dc Represents the actual reference value of the voltage outer loop after adjustment, i L Represents the output inductor current, i * represents the current inner loop reference, u o * Represents the current inner loop output.

[0099] The effect of this method is described below in conjunction with comparative experiments.

[0100] Figure 6a It is a simulation waveform diagram of the DC side output voltage and input current of a three-phase current-type PWM rectifier that is not controlled to the linear modulation region as shown in some embodiments of this specification, Figure 6b The output voltage and input current simulation waveform of the DC side of the three-phase current-type PWM rectifier controlled to the linear modulation area shown in some embodiments of this specification are shown in FIG. an =141.2∠0°, v bn =113.1∠-120°, v cn=141.2∠120° (negative sequence imbalance 7.14%), the DC side output voltage and input current of the rectifier using the duty cycle redistribution algorithm for the three-phase current type PWM rectifier are compared with the rectifier DC side ripple suppression method for input voltage drop recorded in this specification. Figure 6a It can be seen that when the input voltage drops seriously and the rectifier only adopts the unbalanced control strategy to maintain the original output voltage reference value of 200V, the rectifier will work in the overmodulation area for a period of time, resulting in an output voltage ripple of 30V, and the total harmonic distortion (THD) of the three-phase input current is 6.74%, 8.60%, and 7.27% respectively. Figure 6b It can be seen that after adopting the linear modulation area control algorithm, the rectifier output voltage ripple is suppressed to 4.1V, and the three-phase input current waveform is relatively Figure 6a The input current is more sinusoidal and smoother, but due to the large input voltage imbalance and the reduced proportion of the output voltage reference value in the switching function calculation, the total harmonic distortion of the three-phase input current is still large, which is 8.93%, 9.49, and 9.24% respectively. Among them, in order to leave a certain margin, the output voltage reference value is taken as 0.95 times the calculated value.

[0101] Figure 7a is a schematic diagram of simulated waveforms of DC-side output voltage and input current of a three-phase current-type PWM rectifier that is not controlled to the linear modulation region according to some embodiments of this specification, Figure 7b Schematic diagram of the output voltage and input current simulation waveform of the DC side of the three-phase current-type PWM rectifier controlled to the linear modulation area according to some embodiments of this specification, Figure 7a and Figure 7b It can be seen that when the input voltage drops more seriously, the ripple of the output voltage is relatively larger because the rectifier works in the overmodulation area for a larger proportion of the time in a waveform cycle. an =141.2∠0°, v bn =99.0∠-120°, v cn =141.2∠120°, when the negative sequence imbalance is 11.11%, if the original reference voltage is used The rectifier output voltage ripple reached 53.1V, and the total harmonic distortion of the three-phase input current was 7.76%, 7.55% and 6.92% respectively. After adopting the linear modulation area control algorithm, the output voltage ripple was suppressed to 4.3V. However, although the input current was smoother, the total harmonic distortion increased slightly, which were 11.50%, 11.26% and 11.74% respectively. Among them, in order to leave a certain margin, the output voltage reference value was taken as 0.95 times the calculated value.

[0102] Table 3 shows the specific simulation data of the three-phase input current and output voltage ripple of the three-phase current-type PWM rectifier under two unbalanced working conditions using only the duty cycle redistribution algorithm and the linear modulation area control algorithm proposed in this chapter. It can be obtained from the data in the table that when the input voltage drops severely, the rectifier DC side ripple suppression method for input voltage drop recorded in this specification can effectively suppress the output voltage ripple. However, due to the large imbalance of the input voltage and the proportion of the output voltage reference value in the switching function calculation is reduced compared with the original, the total harmonic distortion of the three-phase input current is still large.

[0103] Table 3

[0104]

[0105] In order to verify the correctness of the theoretical analysis of the rectifier DC side ripple suppression method for input voltage drop recorded in this specification and the existing ripple suppression method with an auxiliary circuit, this section builds a simulation model of a three-phase current-type PWM rectifier cascade Buck DC / DC converter in Matlab / Simulink, where the simulation parameters of the three-phase current-type PWM rectifier are shown in Table 4, and the simulation parameters of the Buck DC / DC converter are shown in Table 5.

[0106] Table 4

[0107]

[0108]

[0109] Figure 8a is a schematic diagram of input and output waveforms using an auxiliary circuit ripple suppression strategy according to some embodiments of this specification, Figure 8b is a schematic diagram of input and output waveforms of a linear modulation area control algorithm according to some embodiments of this specification, Figure 8a and Figure 8b It can be seen that the auxiliary circuit is used to suppress the ripple method, and the front-stage three-phase current-type PWM rectifier adopts double closed-loop control. Take 200V, the back-stage Buck converter adopts outer loop PI, inner loop QPR (QuasiProportional Resonant) control, the output voltage reference value Take 175V. The output voltage reference value of the three-phase PWM rectifier using the rectifier DC side ripple suppression method for input voltage drop recorded in this specification Take 175V (to retain a certain margin, take 0.95 times the calculated value in the linear modulation area). Figure 8aAs shown, when the three-phase input voltage drops seriously, under the existing cascade auxiliary circuit method for suppressing the output voltage ripple, the output voltage ripple is suppressed to 2.1V, and the total harmonic distortion of the three-phase input current is: 10.17%, 8.91%, 8.32% respectively. When the rectifier DC side ripple suppression method for input voltage drop recorded in this specification is adopted, the output voltage ripple is suppressed to 4.1V, and the total harmonic distortion of the three-phase input current is: 8.93%, 9.49%, 9.24% respectively. It can be seen that the rectifier DC side ripple suppression method for input voltage drop recorded in this specification and the ripple suppression method of the cascade auxiliary circuit have similar effects on improving the input and output performance of the three-phase current type PWM rectifier when the three-phase input voltage drops seriously.

[0110] Fig. 9 is a module schematic diagram of a rectifier DC side ripple suppression system for input voltage drop according to some embodiments of this specification, such as Fig. 9 As shown, the rectifier DC side ripple suppression system for input voltage drop may include a voltage calculation module, a function calculation module and a suppression control module.

[0111] The voltage calculation module can be used to calculate the three-phase input voltage.

[0112] The function calculation module can be used to calculate the three-phase switching function based on the three-phase input voltage.

[0113] The suppression control module can be used to make overmodulation zone judgment. When it is determined that the command current vector is in the linear modulation area, the output voltage reference value is determined based on the calculation result of the three-phase switching function. Based on the calculation result of the three-phase switching function and the output voltage reference value, the DC side voltage ripple of the three-phase current type PWM rectifier is suppressed.

[0114] The rectifier DC side ripple suppression system for input voltage drop can be used to execute the rectifier DC side ripple suppression method for input voltage drop. For more descriptions of the rectifier DC side ripple suppression system for input voltage drop, please refer to the relevant descriptions of the rectifier DC side ripple suppression method for input voltage drop, which will not be repeated here.

[0115] Finally, it should be understood that the embodiments described in this specification are only used to illustrate the principles of the embodiments of this specification. Other variations may also fall within the scope of this specification. Therefore, as an example and not a limitation, alternative configurations of the embodiments of this specification may be considered consistent with the teachings of this specification. Accordingly, the embodiments of this specification are not limited to the embodiments explicitly introduced and described in this specification.

Claims

1. A method for suppressing ripple on the DC side of a rectifier for input voltage drop, characterized in that: include: Calculate the three-phase input voltage; Based on the three-phase input voltage, calculate the three-phase switching function; Performing overmodulation zone judgment, when it is determined that the command current vector is in the linear modulation area, determining an output voltage reference value based on a calculation result of a three-phase switching function, and suppressing a DC side voltage ripple of a three-phase current-type PWM rectifier based on the calculation result of the three-phase switching function and the output voltage reference value; When the command current vector is in the linear modulation region, the three-phase switching function is: ， in, is the A phase voltage, is the B phase voltage, is the C phase voltage, is the switching function of the three-phase bridge arm, is the switching function of the bridge arm of phase a, is the switching function of the b-phase bridge arm, is the switching function of the c-phase bridge arm, is the output voltage reference value.

2. The method for suppressing ripple on the DC side of a rectifier for input voltage drop according to claim 1, characterized in that: The calculating of the three-phase switching function based on the three-phase input voltage includes: Based on the three-phase input voltage, calculating the duty cycle of the effective current vector and the duty cycle of the zero vector; A three-phase switching function is calculated based on the duty cycle of the effective current vector and the duty cycle of the zero vector.

3. The method for suppressing ripple on the DC side of a rectifier for input voltage drop according to claim 2, characterized in that: The step of determining the output voltage reference value based on the calculation result of the three-phase switching function includes: Calculate the modulation degree based on the target current vector magnitude, the DC side current, the output voltage and the input voltage magnitude; Based on the modulation index, determine the output voltage reference value constraint; The output voltage reference value is calculated based on the calculation result of the three-phase switching function and the output voltage reference value constraint.

4. The method for suppressing ripple on the DC side of a rectifier for input voltage drop according to claim 3, characterized in that: The output voltage reference value constraint is: ， in, is the output voltage reference value, is the amplitude of the positive sequence component of the three-phase input voltage, is the amplitude of the negative sequence component of the three-phase input voltage.

5. The method for suppressing ripple on the DC side of a rectifier for input voltage drop according to claim 3, characterized in that: The step of determining the output voltage reference value constraint based on the modulation index includes: Calculate the margin voltage; Based on the modulation degree and the margin voltage, an output voltage reference value constraint is determined.

6. The method for suppressing ripple on the DC side of a rectifier for input voltage drop according to claim 5, characterized in that: Calculating the margin voltage includes: The margin voltage is calculated based on the switching loss of the power switch tube and the parasitic resistance of the device.

7. The method for suppressing ripple on the DC side of a rectifier for input voltage drop according to claim 6, characterized in that: The calculation formula of the margin voltage is: ， in, is the margin voltage, is the DC side current, is the parasitic resistance of the output filter inductor, is the on-state resistance of the switch tube, is the target current vector value, is the parasitic resistance of the input filter inductor.

8. The method for suppressing ripple on the DC side of a rectifier for input voltage drop according to any one of claims 1 to 7, characterized in that: Based on the calculation result of the three-phase switching function and the output voltage reference value, suppressing the DC side voltage ripple of the three-phase current source PWM rectifier includes: The sampled output voltage and the output voltage reference value are sent to the first PI controller after passing through a comparator to obtain a current inner loop reference value; The current inner loop reference value and the sampled inductor current are sent to the second PI controller through a comparator to obtain the voltage inner loop output; Based on the calculation result of the three-phase switching function and the voltage inner loop output, the DC side voltage ripple of the three-phase current-source PWM rectifier is suppressed.

9. A rectifier DC side ripple suppression system for input voltage drop, characterized in that: include: A voltage calculation module is used to calculate the three-phase input voltage; A function calculation module, used for calculating a three-phase switching function based on a three-phase input voltage; A suppression control module is used to make an overmodulation area judgment, and when it is determined that the command current vector is located in the linear modulation area, an output voltage reference value is determined based on the calculation result of the three-phase switching function, and a DC side voltage ripple of the three-phase current type PWM rectifier is suppressed based on the calculation result of the three-phase switching function and the output voltage reference value; When the command current vector is in the linear modulation region, the three-phase switching function is: ， in, is the A phase voltage, is the B phase voltage, is the C phase voltage, is the switching function of the three-phase bridge arm, is the switching function of the bridge arm of phase a, is the switching function of the b-phase bridge arm, is the switching function of the c-phase bridge arm, is the output voltage reference value.

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