Direct current charging pile module without electrolytic capacitor and output ripple control method thereof

Abstract

The invention discloses a direct current charging pile module without an electrolytic capacitor and an output ripple control method thereof, the direct current charging pile module only adopts a non-electrolytic capacitor, and the output ripple control method comprises a frequency conversion control strategy and an output ripple control strategy. Adjusting the switching period of a switching tube in the post-stage DC / DC converter according to the frequency conversion control strategy; according to the output ripple control strategy, a switching period compensation result is obtained through calculation according to the output ripple change trend, and the switching period of a switching tube in a post-stage DC / DC converter is further adjusted on the basis of frequency conversion control so as to suppress the output ripple. Compared with the prior art, the direct-current charging pile module only adopts the non-electrolytic capacitor, so that the service life and the reliability of the whole direct-current charging pile module are improved; the output of a post-stage DC / DC converter is stabilized near an expected value through a frequency conversion control strategy, and an additional output ripple control strategy is used for solving the problem that the output ripple is relatively large under the condition of no electrolytic capacitor.

Description

Technical Field

[0001] The present invention relates to the technical field of electric vehicles, and in particular to a DC charging pile module without an electrolytic capacitor and an output ripple control method thereof. Background Art

[0002] As the mileage of electric vehicles continues to increase, charging speed is an important factor limiting the development of the electric vehicle industry, and the output power demand for a single DC charging pile module is getting higher and higher. Common charging pile module power levels include 11kW, 22kW and 40kW, etc. The parallel use of multiple DC charging pile modules can greatly increase the total charging power and effectively improve the charging rate of electric vehicle batteries.

[0003] The DC charging pile module is usually a two-stage structure: the front-stage three-phase power factor correction (Power Factor Correction, PFC) rectifier (to achieve AC-DC conversion and power factor correction) and the rear-stage DC / DC converter (to meet the charging requirements of a wide battery voltage range). The front-stage three-phase PFC rectifier rectifies the three-phase power input from the power grid to improve the power factor. The main topological schemes of the front-stage PFC include three-phase six-switch PFC rectifier, three-phase Vienna rectifier and Swiss rectifier, etc. The commonly used control methods include dq decoupling control, three-phase independent control and midpoint potential balance control. The rear-stage DC / DC converter is used to realize voltage level conversion of the output of the three-phase PFC rectifier and has the function of buck-boost. The main topological schemes used in the rear stage are LLC resonant converter, series resonant converter and phase-shifted full-bridge converter, etc. The main control methods used are variable frequency control, variable duty cycle control and phase shift control.

[0004] In traditional solutions, large-capacity electrolytic capacitors are usually used as energy storage capacitors to balance the difference in instantaneous power between the input and output of the vehicle charging power supply. However, the electrolyte inside the electrolytic capacitor is prone to aging and corrosion in high temperature and high voltage environments, causing the capacitance of the electrolytic capacitor to decay, which is an important reason for the failure of the charging pile module and affects the service life and reliability of the charging pile.

[0005] However, the current control strategy cannot solve the problem of large output ripple caused by the absence of electrolytic capacitors. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention proposes a DC charging pile module without electrolytic capacitor and an output ripple control method thereof.

[0007] The technical solution of the present invention is to propose a DC charging pile module without electrolytic capacitors, including a front-stage PFC converter and a rear-stage DC / DC converter, wherein the front-stage PFC converter and the rear-stage DC / DC converter are connected via a bus capacitor;

[0008] The DC charging pile also has a controller for controlling the switching cycle of the subsequent DC / DC converter, and the controller can execute a variable frequency control strategy and an output ripple control strategy;

[0009] The frequency conversion control strategy is used as the main power control to adjust the switching cycle of the switch tube in the subsequent DC / DC converter according to the output electrical parameters of the subsequent DC / DC converter in the DC charging pile;

[0010] The output ripple control strategy is used to obtain the variable corresponding to the ripple change trend in the DC charging pile, and calculate the variable through a control loop to obtain a switching cycle compensation result, so as to further adjust the switching cycle of the switch tube in the subsequent DC / DC converter.

[0011] Further, the front-stage PFC converter includes any of the following rectifiers: a three-phase PWM rectifier, including a three-phase six-switch PFC rectifier, a three-phase Vienna rectifier, and a Swiss rectifier;

[0012] The latter DC / DC converter includes any one of the following converters: LLC resonant converter, series resonant converter and phase-shifted full-bridge converter;

[0013] The common bus of the DC charging pile module without electrolytic capacitor adopts non-electrolytic capacitor as bus capacitor, and the common bus is connected to the bus capacitor.

[0014] The present invention also proposes an output ripple control method for a DC charging pile module without an electrolytic capacitor, the output ripple control method comprising:

[0015] Execute the frequency conversion control strategy and the output ripple control strategy to adjust the switching cycle of the switch tube in the subsequent DC / DC converter; wherein,

[0016] The frequency conversion control strategy specifically obtains the main control quantity DC_PI according to the output electrical parameters of the rear-stage DC / DC converter in the DC charging pile;

[0017] The output ripple control strategy is executed to obtain the variable corresponding to the ripple change trend in the DC charging pile, and the variable is calculated through a control loop to obtain a frequency compensation result, and the sum of the main control quantity DC_PI and the compensation result is used as the final result to jointly determine the switching period of the switch tube in the subsequent DC / DC converter.

[0018] Furthermore, the output electrical parameters include the output voltage V of the subsequent DC / DC converter. o and output current I o .

[0019] Furthermore, the frequency conversion control strategy includes:

[0020] The output voltage V o With the output voltage reference value V o_ref Make a difference and get the first difference value v o_error ;

[0021] The output current I o With the output current reference value I o_ref Make a difference and get the second difference i o_error ;

[0022] The first difference v o_error and the second difference i o_error The smaller value of is used as the output error Output_error, proportional-integral control is performed on the output error Output_error, and the output value of the proportional-integral control is used as the main control quantity DC_PI to adjust the switching period of the switch tube in the subsequent DC / DC converter.

[0023] Furthermore, the output ripple control strategy includes:

[0024] According to the bus voltage v of the bus capacitor bus and the output voltage V o The first variable PART_Ⅰ and the second variable PART_Ⅱ representing the change trends of the two are calculated;

[0025] According to the bus voltage ripple v bus_error , output voltage V o , and the main control variable DC_PI calculates the feedforward variable Forward;

[0026] Calculate a feedforward compensation value Forward_Final according to the first variable PART_I, the second variable PART_II and the feedforward variable Forward;

[0027] The switching period of the switch tube in the subsequent DC / DC converter is determined according to the feedforward compensation value Forward_Final and the main control variable DC_PI.

[0028] Furthermore, the bus voltage v according to the bus capacitor bus and the output voltage V o Before calculating the first variable PART_I and the second variable PART_II that characterize the change trends of the two, it also includes:

[0029] The output error Output_error is low-pass filtered, and the output error Output_error after low-pass filtering is subjected to proportional differential control, and the result of the proportional differential control is used as the first variable PART_I.

[0030] Furthermore, the bus voltage v according to the bus capacitor bus and the output voltage V o Before calculating the first variable PART_I and the second variable PART_II that characterize the change trends of the two, it also includes:

[0031] According to the output voltage V o Calculate bus voltage reference value V bus_ref , the bus voltage v bus With the bus voltage reference value V bus_ref Make a difference and take the difference as the bus voltage ripple v bus_error ;

[0032] According to the bus voltage ripple v bus_error , output voltage V o , and the main control variable DC_PI calculate the feedforward variable Forward, the calculation model is:

[0033]

[0034] Among them, Forward is the feedforward variable, v bus_error is the bus voltage ripple, V o is the output voltage, DC_PI is the main control variable;

[0035] The feedforward variable Forward is low-pass filtered and then its differential value is taken, and the differential value is the second variable PART_II.

[0036] Further, the switching cycle of the switch tube in the subsequent DC / DC converter is determined based on the feedforward compensation value Forward_Final and the main control variable DC_PI, specifically including:

[0037] The first variable PART_I, the second variable PART_II, and the step length Step_k corresponding to the ripple change trend are multiplied and then integrated, and the integration result is used as the feedforward coefficient T_Forward;

[0038] Multiplying the feedforward coefficient T_Forward by the feedforward variable Forward and limiting the amplitude to obtain a feedforward compensation value Forward_Final as the frequency compensation result;

[0039] The sum of the feedforward compensation value Forward_Final and the main control variable DC_PI is used as the final result to adjust the switching period of the switch tube in the subsequent DC / DC converter.

[0040] Compared with the prior art, the present invention has at least the following beneficial effects:

[0041] The present invention can use non-electrolytic capacitors for the bus capacitors in the DC charging pile, so as to adapt to the continuous high-power / cycle standby working mode during supercharging and fast charging. In addition, the present invention can also stabilize the output of the subsequent DC / DC converter to near the desired value through a variable frequency control strategy, and can suppress the output ripple through an output ripple control strategy, which can solve the problem of additional large output ripple caused by the use of non-electrolytic capacitors. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0043] Figure 1 It is the overall principle block diagram of the DC charging pile in the present invention and its control strategy block diagram.

[0044] Figure 2 A circuit topology diagram of a front-stage PFC converter in a first embodiment of the present invention;

[0045] Figure 3 A circuit topology diagram of a front-stage PFC converter in a second embodiment of the present invention;

[0046] Figure 4 A circuit topology diagram of a front-stage PFC converter in a third embodiment of the present invention;

[0047] Figure 5 A circuit topology diagram of a rear-stage DC / DC converter in the first embodiment of the present invention;

[0048] Figure 6 A circuit topology diagram of a rear-stage DC / DC converter in a second embodiment of the present invention;

[0049] Figure 7 A circuit topology diagram of a rear-stage DC / DC converter in a third embodiment of the present invention;

[0050] Figure 8 This is a circuit topology diagram of the DC charging pile in the present invention;

[0051] Fig. 9It is a control block diagram of the frequency conversion control strategy in the present invention;

[0052] Fig.10 It is a control block diagram of the output ripple control strategy in the present invention;

[0053] Fig.11 This is a waveform diagram of the output voltage ripple of a DC charging pile when the output ripple control method of the present invention is not adopted;

[0054] Fig.12 The output voltage ripple waveform of the DC charging pile using the output ripple control method of the present invention;

[0055] Fig.13 This is a waveform diagram of the output current ripple of a DC charging pile when the output ripple control method of the present invention is not adopted;

[0056] Fig.14 The output current ripple waveform of the DC charging pile using the output ripple control method of the present invention;

[0057] Fig.15 It is a schematic diagram of the dynamic process of output voltage ripple suppression in the present invention;

[0058] Fig.16 It is a schematic diagram of the dynamic process of output current ripple suppression in the present invention. DETAILED DESCRIPTION

[0059] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0060] Thus, a feature indicated in this specification will be used to illustrate one of the features of an embodiment of the present invention, rather than implying that each embodiment of the present invention must have the described feature. In addition, it should be noted that this specification describes many features. Although some features can be combined together to illustrate possible system designs, these features can also be used in other combinations that are not explicitly described. Thus, unless otherwise stated, the described combinations are not intended to be limiting.

[0061] The principle and structure of the present invention are described in detail below with reference to the accompanying drawings and embodiments.

[0062] In traditional solutions, large-capacity electrolytic capacitors are usually used as energy storage capacitors to balance the difference in instantaneous power between the input and output of the vehicle charging power supply. However, the electrolyte inside the electrolytic capacitor is prone to aging and corrosion in high temperature and high voltage environments, causing the capacitance of the electrolytic capacitor to decay, which is an important reason for the failure of the charging pile module and affects the service life and reliability of the charging pile.

[0063] For the above questions, please see Figure 1 The DC charging pile module proposed in the present invention includes: a front-stage PFC converter, a rear-stage DC / DC converter, the non-electrolytic capacitor used, and a control strategy adopted for the topology.

[0064] Among them, the input end of the front-stage PFC converter is connected to the three-phase alternating current of the power grid.

[0065] The input end of the subsequent DC / DC converter is connected to the output end of the previous PFC converter.

[0066] The front-stage PFC converter and the rear-stage DC / DC converter are electrically connected in parallel through non-electrolytic capacitors, and the output capacitor and the filter capacitor also use non-electrolytic capacitors.

[0067] The beneficial effects of the above design are:

[0068] The entire two-stage DC charging pile does not use electrolytic capacitors, but adopts non-electrolytic capacitors as two-stage output filter capacitors, which effectively improves the life and reliability of the DC charging pile.

[0069] Specifically, the DC charging pile proposed in the present invention also has a controller for controlling the switching cycle of the subsequent DC / DC converter, and the controller can execute a variable frequency control strategy and an output ripple control strategy;

[0070] And the frequency conversion control strategy is used as the main power control to adjust the switching cycle of the switch tube in the subsequent DC / DC converter according to the output electrical parameters of the subsequent DC / DC converter in the DC charging pile;

[0071] The output ripple control strategy is used to obtain the variable corresponding to the ripple change trend in the DC charging pile, and calculate the variable through the control loop to obtain the switching cycle compensation result, which is used to further adjust the switching cycle of the switching tube in the subsequent DC / DC converter.

[0072] The front-stage PFC converter includes any of the following rectifiers: a three-phase six-switch PFC rectifier, a three-phase Vienna rectifier, and a Swiss rectifier. Figure 2 , Figure 3 , Figure 4 They are circuit topology diagrams of the front-stage PFC converter using the above three-phase six-switch PFC rectifier, three-phase Vienna rectifier and Swiss rectifier;

[0073] The subsequent DC / DC converter includes any of the following converters: LLC resonant converter, series resonant converter and phase-shifted full-bridge converter. Figure 5 , Figure 6 , Figure 7 They are circuit topology diagrams of the subsequent DC / DC converter using the above-mentioned LLC resonant converter, series resonant converter and phase-shifted full-bridge converter.

[0074] The above-mentioned electrolytic capacitor mainly refers to the common bus portion of the two-stage topology, which uses a non-capacitive capacitor as a bus capacitor, and the common bus is connected to the bus capacitor.

[0075] Figure 8 This is a circuit topology diagram of a DC charging pile under a preferred embodiment of the present invention. In this embodiment, a three-phase four-wire Vienna converter topology is used as a front-stage PFC converter to perform three-phase rectification and active power factor correction, and provide input voltage for a rear-stage DC / DC converter; a three-phase interleaved parallel LLC resonant converter topology is used as a rear-stage DC / DC converter to adjust the output voltage; and a non-electrolytic capacitor is used to connect the three-phase four-wire Vienna converter to the three-phase interleaved parallel LLC converter.

[0076] like Figure 8 As shown, the three-phase four-wire Vienna rectifier circuit includes three boost inductors L 1 ~L 3 , three filter capacitors C 1 ~C 3 , six fast recovery diodes D 1 ~D 6 , three groups of switches S consisting of two field effect transistors with reverse diodes connected in series in reverse 1 ~S 3 And two sets of non-electrolytic capacitors C s1 and C s2 ; The three-phase power grid is connected to three boost inductors L 1 ~L 3 One end of the three boost inductors L 1 ~L 3 The other end is connected to the fast recovery diode D 1 , D 3 and D 5 The anode and filter capacitor C 1 ~C 3 The upper end of the fast recovery diode D 1 The anode and D 2 The cathode of the fast recovery diode D 3 The anode and D 4 The cathode of the fast recovery diode D 5The anode and D 6 The cathode of the fast recovery diode D 1 , D 3 and D 5 The cathode of the fast recovery diode D 2 , D 4 and D 6 The anode of the fast recovery diode D 1 , D 3 and D 5 The anodes of the three switches S 1 ~S 3 One end of the switch S 1 ~S 3 The other end is then connected to the non-electrolytic capacitor C s1 The lower end of the non-electrolytic capacitor C s2 The upper end is connected to the non-electrolytic electrode C s1 The upper end of the fast recovery diode D 5 The cathode of the non-electrolytic electrode is connected to s2 The lower end of the fast recovery diode D 6 The anode of the non-electrolytic capacitor C s1 With C s2 The midpoint of the filter capacitor C 1 ~C 3 The lower end is connected.

[0077] The LLC resonant converter consists of six field effect transistors P 1 ~P 6 , three resonant inductors L r1 ~L r3 , three resonant capacitors C r1 ~C r3 , three excitation inductors L m1 ~L m3 , three single-phase transformers T 1 ~T 3 , six fast recovery diodes D 7 ~D 12 and output capacitor C o ; 6 field effect transistors P 1 ~P 6 The three-phase full-bridge inverter circuit is composed of field effect transistor P 1 , P 3 and P 5 The drain of the field effect transistor P 2 , P 4 and P 6 The source of the field effect transistor P 1 The drain of the three-phase four-wire Vienna converter output terminal non-electrolytic capacitor Cs1 The upper end of the field effect transistor P 2 The source and non-electrolytic capacitor C s2 The lower end of the field effect transistor P 1 The source and P 2 The drain of the field effect transistor P 3 The source and P 4 The drain of the field effect transistor P 5 The source and P 6 The drain of the field effect transistor P 1 , P 3 and P 5 The source of r1 , L r2 and L r3 One end of the resonant inductor L r1 , L r2 and L r3 The other end is connected to the resonant capacitor C r1 , C r2 and C r3 One end of the resonant capacitor C r1 , C r2 and C r3 The other end is connected to the single-phase transformer T 1 ~T 3 The same-name terminals on the primary side are connected, and the single-phase transformer T 1 , T 2 and T 3 The opposite ends of the primary side are connected together, and the excitation inductance L m1 ~L m3 Respectively with single-phase transformer T 1 ~T 3 The primary windings of the single-phase transformer T 1 ~T 3 The same-name end of the secondary winding is connected to the fast recovery diode D 7 , D 9 and D 11 The anode of the fast recovery diode D 7 The anode and D 8 The cathode of the fast recovery diode D 9 The anode and D 10 The cathode of the fast recovery diode D 11 The anode and D 12 The cathode of the fast recovery diode D 7 , D 9 and D 11 The cathode of the fast recovery diode D 8 , D 10 and D 12The anode of the fast recovery diode D 7 ~D 12 It forms a three-phase uncontrolled rectifier bridge, and finally outputs the capacitor C o Connect fast recovery diode D 11 The cathode and D 12 anode.

[0078] Through the above configuration, the present invention adopts a solution of non-electrolytic capacitors (such as film capacitors, ceramic capacitors, etc.), which can improve the service life and reliability of the entire DC charging pile.

[0079] In addition, after the busbar capacitor is set as a non-electrolytic capacitor, there are still problems in the existing technology. The current super charging pile has continuous high-power / standby cycle operation. Electrolytic capacitors are very unreliable in this application condition, so a non-electrolytic capacitor solution is needed. However, the use of non-electrolytic capacitors will inevitably bring about output ripple problems. The current control strategy cannot solve the large output ripple caused by the absence of electrolytic capacitors.

[0080] Based on the above problems, the present invention proposes an output ripple control method for a DC charging pile module without electrolytic capacitors, which includes:

[0081] Execute the variable frequency control strategy and the output ripple control strategy to adjust the switching cycle of the switch tube in the subsequent DC / DC converter; wherein,

[0082] The frequency conversion control strategy is specifically to obtain the main control quantity DC_PI according to the output electrical parameters of the rear-stage DC / DC converter in the DC charging pile;

[0083] The output ripple control strategy is executed to obtain the variables corresponding to the ripple change trend in the DC charging pile, and the variables are calculated through the control loop to obtain the frequency compensation result. The sum of the main control quantity DC_PI and the compensation result is used as the final result to jointly determine the switching period of the switch tube in the subsequent DC / DC converter.

[0084] The variable frequency control strategy provided in the present invention can stabilize the output of the subsequent DC / DC converter near the desired value, and can suppress the output ripple through the output ripple control strategy, thereby achieving the purpose of reducing the output ripple.

[0085] The following is combined with Fig. 9 , the specific process of the frequency conversion control strategy in the present invention is described:

[0086] In the above variable frequency control strategy, the output electrical parameter is the output voltage V of the subsequent DC / DC converter. o and output current I o The present invention can collect the output voltage V o and output current Io To adjust the switching frequency of the switch tube in the subsequent DC / DC converter, so as to stabilize the output near the desired value.

[0087] like Fig. 9 As shown, the specific method of the above variable frequency control strategy includes:

[0088] The output voltage V o With the output voltage reference value V o_ref Make a difference and get the first difference value v o_error ;

[0089] The output current I o With the output current reference value I o_ref Make a difference and get the second difference i o_error ;

[0090] The first difference v o_error and the second difference i o_error The smaller value of is used as the output error Output_error, and proportional-integral control is performed on the output error Output_error. The output value of the proportional-integral control is used as the main control quantity DC_PI to adjust the switching period of the switch tube in the subsequent DC / DC converter.

[0091] Through the above control process, the present invention can stabilize the output of the subsequent DC / DC converter near the desired value.

[0092] The following is combined with Fig.10 , the specific process of the output ripple control strategy in the present invention is described:

[0093] From this attachment Fig.10 It can be seen that the output ripple control strategy is a further action performed based on the above-mentioned frequency conversion control strategy, which can further adjust the switching frequency of the switch tube in the subsequent DC / DC converter to suppress the output ripple, thereby achieving the purpose of reducing the output ripple.

[0094] Among them, the logic of the above output ripple control strategy is:

[0095] According to the bus voltage v of the bus capacitor bus and output voltage V o The first variable PART_Ⅰ and the second variable PART_Ⅱ representing the change trends of the two are calculated;

[0096] According to the bus voltage ripple v bus_error , output voltage V o , and the main control variable DC_PI calculates the feedforward variable Forward;

[0097] Calculate the feedforward compensation value Forward_Final according to the first variable PART_Ⅰ, the second variable PART_Ⅱ and the feedforward variable Forward;

[0098] The switching period of the switch tube in the subsequent DC / DC converter is determined based on the feedforward compensation value Forward_Final and the main control quantity DC_PI.

[0099] In this logic, the output voltage V o The main control quantity DC_PI of proportional integral control is the value detected or calculated in the variable frequency control strategy. Therefore, the above output ripple control strategy needs to be further adjusted based on the above variable frequency control strategy, and only the bus voltage v of the bus capacitor needs to be re-collected. bus That's it.

[0100] Among them, the first variable PART_Ⅰ and the second variable PART_Ⅱ are obtained by the above bus voltage v bus , output voltage V o , and the main control variable DC_PI are calculated. The calculation process of the first variable PART_Ⅰ and the second variable PART_Ⅱ are described below respectively;

[0101] According to the bus voltage v of the bus capacitor bus and output voltage V o Before calculating the first variable PART_I and the second variable PART_II that characterize the change trends of the two, it also includes:

[0102] The output error Output_error is low-pass filtered, and the output error Output_error after low-pass filtering is proportionally differential controlled, and the result of the proportional differential control is used as the first variable PART_Ⅰ.

[0103] Here, the output error Output_error corresponds to the main control quantity DC_PI of the proportional integral control, which is the output parameter obtained in the variable frequency control strategy. Through the above steps, the output voltage V can be obtained. o The first variable of the ripple change trend PART_Ⅰ.

[0104] According to the bus voltage v of the bus capacitor bus and output voltage V o Before calculating the first variable PART_I and the second variable PART_II that characterize the change trends of the two, it also includes:

[0105] According to the output voltage V o Calculate bus voltage reference value V bus_ref , the bus voltage v bus and bus voltage reference value Vbus_ref Make a difference and use the difference as the bus voltage ripple v bus_error ;

[0106] According to the bus voltage ripple v bus_error , output voltage V o , and the main control variable DC_PI calculate the feedforward variable Forward, the calculation model is:

[0107]

[0108] Among them, Forward is the feedforward variable, v bus_error is the bus voltage ripple, V o is the output voltage, DC_PI is the main control variable;

[0109] The feedforward variable Forward is low-pass filtered and its differential value is taken. The differential value is the second variable PART_II.

[0110] Here, the second variable PART_II is only related to the feedforward variable Forward, which is in turn determined by the bus voltage ripple v bus_error , output voltage V o , and the main control quantity DC_PI. Since the output ripple control strategy is a further adjustment based on the variable frequency control strategy, the output voltage V o and the main control variable DC_PI are known values ​​obtained by the variable frequency control strategy, then only the bus voltage ripple v bus_error The corresponding feedforward variable Forward can be obtained, which is then used for filtering and differentiation to obtain the second variable PART_II.

[0111] The above bus voltage ripple v bus_error That is, through the output voltage V o Calculate bus voltage reference value V bus_ref , and the bus voltage v bus and bus voltage reference value V bus_ref Make a difference to get;

[0112] Here, the output voltage reference value V o_ref It is a reference value set according to actual needs. It is a known quantity. When the structure of the DC charger is determined, the bus voltage reference value V can be determined according to the primary-secondary turns ratio of the transformer in the subsequent DC / DC converter and the output gain of the primary-secondary circuit. bus_ref ;

[0113] Bus voltage ripple v bus_error The essence is the actual bus voltage v bus Deviation from bus voltage reference value V bus_refvalue, so only the bus voltage v bus and bus voltage reference value V bus_ref By making a difference, we can get the bus voltage ripple v mentioned above. bus_error .

[0114] The bus voltage ripple v is obtained by this method bus_error After that, combined with the output voltage v o The feedforward variable Forward and the main control variable DC_PI can be obtained through the above calculation model, and then the second variable PART_II can be obtained.

[0115] After the first variable PART_I and the second variable PART_II are calculated through the above logic, the switching cycle of the switch tube in the final post-stage DC / DC converter can be determined in combination with the main control quantity DC_PI obtained by the variable frequency control strategy to achieve the purpose of suppressing the output ripple.

[0116] Here, the specific process of "determining the switching cycle of the switch tube in the subsequent DC / DC converter according to the feedforward compensation value Forward_Final and the main control quantity DC_PI" in the above logic is:

[0117] The first variable PART_I, the second variable PART_II, and the step length Step_k corresponding to the ripple change trend are multiplied and then integrated, and the integration result is used as the feedforward coefficient T_Forward;

[0118] Multiplying the feedforward coefficient T_Forward by the feedforward variable Forward and limiting the amplitude to obtain the feedforward compensation value Forward_Final as the frequency compensation result;

[0119] The sum of the feedforward compensation value Forward_Final and the main control quantity DC_PI is used as the final result to adjust the switching period of the switch tube in the subsequent DC / DC converter.

[0120] Here, the main idea of ​​the output ripple control strategy is to control according to the ripple change trend of the bus voltage and the ripple change trend of the output voltage. When the output ripple control is not turned on, the bus voltage ripple pulsation trend is the same as the output ripple pulsation trend. According to this feature, the control loop can be designed to compensate the output of the frequency conversion control loop, so that the operating frequency of the subsequent switching tube can follow the change of the bus voltage ripple, thereby offsetting the output ripple and achieving the effect of reducing the output ripple.

[0121] In order to reduce the output voltage ripple and control the DC charging pile module to operate at the desired output voltage, the overall process of the present invention is described below by taking the working condition of adjusting the output current of the DC charging pile through the CC load as an example:

[0122] Step 1: Connect the output end of the DC charging pile to the CC load and sample the output voltage V of the DC charging pile. o and output current I o , input the sampled output electrical parameters into the DSP, and the host computer sets the output voltage reference value V o_ref and the output current reference value I o_ref ;

[0123] Step 2: Perform frequency conversion control loop calculation in DSP, using the output voltage reference value V o_ref Subtract the output voltage V o Get the first difference v o_error , using the output current reference value I o_ref Subtract the output current I o Get the second difference i o_error ;

[0124] Step 3: Compare the first difference v o_error and the second difference i o_error The size of the first difference v o_error and the second difference i o_error The smaller value of is taken as the output error Output_error, and the output error Output_error is subjected to proportional integral control, and the output value of the proportional integral control is taken as the main control quantity DC_PI corresponding to the switching cycle of the switch tube in the subsequent DC / DC converter when no compensation is performed;

[0125] Step 4: Sample the bus voltage v output by the DC charging pile bus ;

[0126] Step 5: According to the output voltage reference value V sent by the host computer o_ref Calculate the bus voltage reference value V bus_ref ;

[0127] Step 6: Use bus voltage reference value V bus_ref Subtract the actual bus voltage obtained by sampling bus Get the bus voltage error, that is, the bus voltage ripple v bus_error ;

[0128] Step 7: Use the output voltage reference value V o_ref Subtract the output voltage v o Get the first difference v o_error ;

[0129] Step 8: Perform proportional differential operation on the output error Output_error to obtain a first variable PART_I related to the ripple variation trend of the output voltage;

[0130] Step 9: Use the following calculation model to calculate the required feedforward variable Forward;

[0131]

[0132] Step 10: Differentiating the filtered feedforward variable Forward can obtain the second variable PART_II related to the change trend of the bus voltage ripple;

[0133] Step 11: Multiply the obtained first variable PART_I by the second variable PART_II and the step length Step_k and add them together to obtain the feedforward coefficient T_Forward;

[0134] Step 12: Multiply the feedforward coefficient T_Forward and the feedforward variable Forward and then limit them to obtain the final feedforward compensation value Forward_Final. The physical meaning of the feedforward compensation value Forward_Final is the switching duty cycle of the output ripple control loop that needs to be compensated to the variable frequency control loop;

[0135] Step 13: Add the main control quantity DC_PI of the proportional integral control calculated in step 3 and the feedforward compensation value Forward_Final calculated in step 12 to obtain the final duty cycle PRD of the switch tube in the subsequent DC / DC converter. The DSP sends a switching signal corresponding to the switching frequency to control the switch tube of the subsequent DC / DC converter.

[0136] like Fig.11 As shown, when the variable frequency control strategy is not turned on, the switching frequency of the subsequent DC / DC converter is only calculated by the variable frequency control loop, and the variable frequency control loop cannot respond to the high-frequency pulsation of the bus voltage ripple, resulting in an increase in the output voltage ripple of the subsequent DC / DC converter, and the pulsation trend of the output voltage ripple is the same as the pulsation trend of the bus voltage ripple. The product of the first variable PART_I and the second variable PART_II is greater than 0, and the feedforward coefficient T_Forward calculated in step 11 increases; when the pulsation trend of the output voltage ripple is opposite to that of the bus voltage, the product of the first variable PART_I and the second variable PART_II is less than 0, and the feedforward coefficient T_Forward calculated in step 11 decreases.

[0137] When the bus voltage v bus Greater than bus voltage reference value V bus_ref When the bus voltage ripple v bus_erroris less than 0, the feedforward variable Forward calculated in step 9 is less than 0, the feedforward compensation value Forward_Final calculated in step 12 is less than 0, and the final duty cycle PRD of the switch tube in the subsequent DC / DC converter is reduced, that is, the operating frequency of the switch tube is increased, which suppresses the increase of the output voltage;

[0138] When the bus voltage v bus Less than bus voltage reference value V bus_ref When the bus voltage ripple v bus_error is greater than 0, the feedforward variable Forward calculated in step 9 is greater than 0, the feedforward compensation value Forward_Final calculated in step 12 is greater than 0, and the final duty cycle PRD of the switch tube in the subsequent DC / DC converter increases, that is, the operating frequency of the switch tube decreases, suppressing the reduction of the output voltage ripple. Fig.12 As shown, the output voltage ripple is very small when stability is achieved, meeting the corresponding requirements.

[0139] Regarding reducing the output current ripple, the specific implementation process is the same as the above process, and will not be described in detail here.

[0140] Fig.13 and Fig.14 They are respectively an output current ripple waveform diagram of a DC charging pile without adopting the output ripple control method in the present invention and an output current ripple waveform diagram of a DC charging pile with adopting the output ripple control method in the present invention. Their changing trends are the same as those of the output voltage ripple waveform diagram, and they will not be repeated here.

[0141] Compared with the prior art, the present invention has at least the following beneficial effects:

[0142] The present invention can use non-electrolytic capacitors for the bus capacitors in the DC charging pile, so as to adapt to the continuous high-power / cycle standby working mode during supercharging and fast charging. In addition, the present invention can also stabilize the output of the subsequent DC / DC converter to near the desired value through a variable frequency control strategy, and can suppress the output ripple through an output ripple control strategy, which can solve the problem of additional large output ripple caused by the use of non-electrolytic capacitors.

[0143] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A DC charging pile module without electrolytic capacitor, characterized in that: It includes a front-stage PFC converter and a rear-stage DC / DC converter, wherein the front-stage PFC converter and the rear-stage DC / DC converter are connected via a bus capacitor; The DC charging pile also has a controller for controlling the switching cycle of the subsequent DC / DC converter, and the controller can execute a variable frequency control strategy and an output ripple control strategy; The frequency conversion control strategy is used as the main power control to adjust the switching cycle of the switch tube in the subsequent DC / DC converter according to the output electrical parameters of the subsequent DC / DC converter in the DC charging pile; The output ripple control strategy is used to obtain the variable corresponding to the ripple change trend in the DC charging pile, and calculate the variable through a control loop to obtain a switching cycle compensation result, so as to further adjust the switching cycle of the switch tube in the subsequent DC / DC converter.

2. The DC charging pile module without electrolytic capacitor according to claim 1, characterized in that: The front-stage PFC converter includes any of the following rectifiers: a three-phase PWM rectifier, including a three-phase six-switch PFC rectifier, a three-phase Vienna rectifier, and a Swiss rectifier; The latter DC / DC converter includes any one of the following converters: LLC resonant converter, series resonant converter and phase-shifted full-bridge converter; The common bus of the DC charging pile module without electrolytic capacitor adopts non-electrolytic capacitor as bus capacitor, and the common bus is connected to the bus capacitor.

3. A method for controlling output ripple of a DC charging pile module without electrolytic capacitor according to any one of claims 1 to 2, characterized in that: The output ripple control method comprises: Execute the frequency conversion control strategy and the output ripple control strategy to adjust the switching cycle of the switch tube in the subsequent DC / DC converter; wherein, The frequency conversion control strategy is specifically to obtain the main control quantity DC_PI according to the output electrical parameters of the rear-stage DC / DC converter in the DC charging pile; The output ripple control strategy is executed to obtain the variable corresponding to the ripple change trend in the DC charging pile, and the variable is calculated through a control loop to obtain a frequency compensation result, and the sum of the main control quantity DC_PI and the compensation result is used as the final result to jointly determine the switching period of the switch tube in the subsequent DC / DC converter.

4. The output ripple control method according to claim 3, characterized in that: The output electrical parameters include the output voltage V of the subsequent DC / DC converter o and output current I o .

5. The output ripple control method according to claim 4, characterized in that: The frequency conversion control strategy includes: The output voltage V o With the output voltage reference value V o_ref Make a difference and get the first difference value v o_error ; The output current I o With the output current reference value I o_ref Make a difference and get the second difference i o_error ; The first difference v o_error and the second difference i o_error The smaller value of is used as the output error Output_error, proportional-integral control is performed on the output error Output_error, and the output value of the proportional-integral control is used as the main control quantity DC_PI to adjust the switching period of the switch tube in the subsequent DC / DC converter.

6. The output ripple control method according to claim 5, characterized in that: The output ripple control strategy includes: According to the bus voltage v of the bus capacitor bus and the output voltage V o Calculate the first variable PART_I and the second variable PART_II that represent the change trends of the two; According to the bus voltage ripple v bus_error , output voltage V o , and the main control variable DC_PI calculates the feedforward variable Forward; Calculate a feedforward compensation value Forward_Final according to the first variable PART_I, the second variable PART_II and the feedforward variable Forward; The switching period of the switch tube in the subsequent DC / DC converter is determined according to the feedforward compensation value Forward_Final and the main control variable DC_PI.

7. The output ripple control method according to claim 6, characterized in that: The bus voltage v according to the bus capacitor bus and the output voltage V o Before calculating the first variable PART_I and the second variable PART_II that characterize the change trends of the two, it also includes: The output error Output_error is low-pass filtered, and the output error Output_error after low-pass filtering is subjected to proportional differential control, and the result of the proportional differential control is used as the first variable PART_I.

8. The output ripple control method according to claim 6, characterized in that: The bus voltage v according to the bus capacitor bus and the output voltage V o Before calculating the first variable PART_I and the second variable PART_II that characterize the change trends of the two, it also includes: According to the output voltage V o Calculate bus voltage reference value V bus_ref , the bus voltage v bus With the bus voltage reference value V bus_ref Make a difference and take the difference as the bus voltage ripple v bus_error ; According to the bus voltage ripple v bus_error , output voltage V o , and the main control variable DC_PI calculate the feedforward variable Forward, the calculation model is: Among them, Forward is the feedforward variable, v bus_error is the bus voltage ripple, V o is the output voltage, DC_PI is the main control variable; The feedforward variable Forward is low-pass filtered and then its differential value is taken, and the differential value is the second variable PART_II.

9. The output ripple control method according to claim 6, characterized in that: Determining the switching cycle of the switch tube in the subsequent DC / DC converter according to the feedforward compensation value Forward_Final and the main control quantity DC_PI specifically includes: The first variable PART_I, the second variable PART_II, and the step length Step_k corresponding to the ripple change trend are multiplied and then integrated, and the integration result is used as the feedforward coefficient T_Forward; Multiplying the feedforward coefficient T_Forward by the feedforward variable Forward and limiting the amplitude to obtain a feedforward compensation value Forward_Final as the frequency compensation result; The sum of the feedforward compensation value Forward_Final and the main control variable DC_PI is used as the final result to adjust the switching period of the switch tube in the subsequent DC / DC converter.

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