A control method for AC side high frequency soft start circuit

Abstract

The invention discloses a control method for an AC side high-frequency soft-start circuit. The soft-start circuit comprises an AC side power grid, a switch circuit, a DC side capacitive load, an AC / DC converter unit and a controller. The switch circuit comprises a main switch K1, a soft-start switch K2 connected in parallel therewith and a soft-start resistor R1. The AC / DC converter unit is arranged between the switch circuit and the capacitive load. The controller regulates the main switch K1 and the soft-start switch K2 according to the detected DC side port voltage. The invention detects the DC port voltage to perform high-frequency switching on and off of the AC side soft-start branch. After repeated charging cycles, when the DC port voltage reaches a suitable value, the AC side main circuit relay is closed to achieve the effect of using a small resistance value to carry a large capacitive load. The soft-start branch operates at a maximum power point during the entire charging cycle, thereby reducing the size and cost of the soft-start branch and realizing the engineering application of the capacitive load.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic power systems, and in particular to a control method for an AC side high frequency soft starting circuit. Background Art

[0002] In the existing energy storage microgrid environment, the internal block diagram of the module in the bidirectional converter is as follows: Figure 1 As shown in the figure, when there is a large capacitive load on the DC side, the soft start resistor on the AC side is continuously turned on during the startup process and will be damaged due to overpower. If you need to start the machine with a large capacitive load, you need to choose a larger power soft start resistor or connect multiple resistors in series and parallel, which makes the design cost high and the design size large, which is not suitable for engineering applications.

[0003] Therefore, how to solve the above technical problems is the research direction that technicians in this field are committed to. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a control method for an AC side high frequency soft start circuit.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a control method of an AC side high-frequency soft start circuit, wherein the soft start circuit includes an AC side power grid, a switch circuit, a DC side capacitive load, an AC / DC converter unit and a controller, wherein the switch circuit includes a main switch K1 and a soft start switch K2 and a soft start resistor R1 connected in parallel therewith; the AC / DC converter unit is arranged between the switch circuit and the capacitive load, and the controller regulates the main switch K1 and the soft start switch K2 according to the detected DC side port voltage, and the specific process is as follows:

[0006] 1) The controller is powered;

[0007] 2) Carry out the first cycle of charging, the charging cycle is t1:

[0008] 21) The controller sends a command to the switch circuit to close the soft start switch K2 for a duration of t 1_on , and then disconnect the soft start switch K2, the disconnection time is t 1_off , t1=t 1_on +t 1_off ;

[0009] 22) The controller detects whether the DC side port voltage has reached the maximum charging value U max , and whether the pressure difference between the two is less than the set value. If both conditions are met, a command is issued to the switch circuit to close the main switch K1; if one of them is not met, go to step 3);

[0010] 3) Carry out the second cycle of charging, the charging cycle is t2:

[0011] 31) The controller sends a command to the switch circuit to close the soft start switch K2 for a closing time of t 2_on , and then disconnect the soft start switch K2, the disconnection time is t 2_off , t2=t 2_on+ t 2_off ;

[0012] 32) The controller detects whether the DC side port voltage has reached the maximum charging value U max , and whether the voltage difference between the two is less than the set value. If both conditions are met, a command is issued to the switch circuit to close the main switch K1; if one of them is not met, steps 31)-32) are repeated until the DC side port voltage reaches the maximum charging value U max , close the main switch K1 and complete the soft start.

[0013] As a specific implementation, in step 2), t1 is calculated by formula 1:

[0014]

[0015] t 1_on Calculated by formula 2,

[0016]

[0017] Among them, U0=0, U c1 is the DC side port voltage detected by the controller at the end of the first cycle charging, τ is the charging time constant, e represents the natural constant; C is the subsequent capacitive load, P1 is the impact power that the soft start resistor can withstand within t1 time, U rms is the AC side grid voltage,

[0018] In step 3), t2 is calculated by formula 3:

[0019]

[0020] t 2_on Calculated by formula 4,

[0021]

[0022] Among them, U c2 P2 is the DC side port voltage detected by the controller at the end of the second cycle charging, and P3 is the impact power that the soft start resistor can withstand during the time t2.

[0023] As a specific implementation, the calculation formula of the charging time constant τ is: τ=R×C, R is the resistance value of the soft start resistor R1, and C is the subsequent capacitive load.

[0024] Due to the application of the above technical scheme, the present invention has the following advantages compared with the prior art: the control method of the present invention detects the DC port voltage to high-frequency switch the AC side soft start branch, and after repeated cycles, when the DC port voltage reaches an appropriate value, the AC side main circuit relay is closed, so as to achieve the effect of using a small resistance to carry a large capacitive load. The soft start branch works at the maximum power point during the entire charging cycle, reducing the size and cost of the soft start branch, and realizing the engineering application of capacitive loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Design electrical principle block diagram for soft start mentioned in the prior art;

[0026] Figure 2 An electrical principle block diagram for the soft start design of the present invention;

[0027] Figure 3 The figure is a timing logic flow chart of the soft start process described in the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0029] The present invention provides a control method for an AC side high frequency soft start circuit. Figure 2 As shown, it includes an AC side power grid, a switching circuit, a DC side capacitive load, an AC / DC converter unit and a controller. The switching circuit includes a main switch K1 and a soft start switch K2 and a soft start resistor R1 connected in parallel therewith. The AC / DC converter unit is arranged between the switching circuit and the capacitive load. The controller regulates the main switch K1 and the soft start switch K2 according to the detected DC side port voltage.

[0030] The specific process is as follows:

[0031] 1) The controller is powered;

[0032] 2) Carry out the first cycle of charging, the charging cycle is t1:

[0033] 21) The controller sends a command to the switch circuit to close the soft start switch K2 for a closing time of t 1_on , and then disconnect the soft start switch K2, the disconnection time is t 1_off , t1=t 1_on +t 1_off ;

[0034] 22) The controller detects whether the DC side port voltage has reached the maximum charging value U max, and whether the pressure difference between the two is less than the set value. If both conditions are met, a command is issued to the switch circuit to close the main switch K1; if one of them is not met, go to step 3);

[0035] 3) Carry out the second cycle of charging, the charging cycle is t2:

[0036] 31) The controller sends a command to the switch circuit to close the soft start switch K2 for a closing time of t 2_on , and then disconnect the soft start switch K2, the disconnection time is t 2_off , t2=t 2_on +t 2_off ;

[0037] 32) The controller detects whether the DC side port voltage has reached the maximum charging value U max , and whether the voltage difference between the two is less than the set value. If both conditions are met, a command is issued to the switch circuit to close the main switch K1; if one of them is not met, steps 31)-32) are repeated until the DC side port voltage reaches the maximum charging value U max , close the main switch K1 and complete the soft start.

[0038] Here, in step 2), t1 is calculated by formula 1,

[0039]

[0040] t 1_on Calculated by formula 2,

[0041]

[0042] Among them, U0=0, U c1 is the DC side port voltage detected by the controller at the end of the first cycle charging, τ is the charging time constant, e represents the natural constant; C is the subsequent capacitive load, P1 is the impact power that the soft start resistor can withstand within t1 time, U rms is the AC side grid voltage,

[0043] In step 3), t2 is calculated by formula 3:

[0044]

[0045] t 2_on Calculated by formula 4,

[0046]

[0047] Among them, U c2P2 is the DC side port voltage detected by the controller at the end of the second cycle charging, and P3 is the impact power that the soft start resistor can withstand during the time t2.

[0048] The calculation formula of the charging time constant τ is: τ=R×C, R is the resistance value of the soft start resistor R1, and C is the capacitive load of the subsequent stage.

[0049] Example

[0050] A specific embodiment is provided below.

[0051] In the embodiment, the system rear capacitive load is C = 0.01F, the soft start resistor is given as R = 100Ω / 10W, the soft start resistor has a surge power consumption of 200ms and a withstand power of 4 times the rated power, and the grid voltage is U g =220V; the final charging voltage is the maximum charging voltage Here, Ug is U rms , the voltage difference setting value is 20V.

[0052] The soft start process includes:

[0053] The controller is powered on and charged for the first time.

[0054] The first charging cycle is t1 = 400ms, and the soft start branch closing time is t 1_on =200ms, the soft start branch disconnection time is t 1_off = 200ms, the capacitor terminal voltage is charged to At this time, the average power consumption of the resistor during the t1 period is P R (t1) = 39.759W, the voltage does not meet the requirement that the difference between the final charging voltage and the actual voltage is ≤ 20V, and the second charging cycle continues;

[0055] The second charging cycle is t2 = 900ms, and the soft start branch closing time is t 2_on =200ms, the soft start branch disconnection time is t 2_off =700ms, the capacitor terminal voltage is charged to At this time, the average power consumption of the resistor during the t2 period is P R (t2) = 40.78W, the voltage does not meet the requirement that the difference between the final charging voltage and the actual voltage is ≤ 20V, and the third charging cycle is continued;

[0056] The third charging cycle is t3 = 1100ms, and the closing time of the soft start branch is t 3_on =200ms, the soft start branch disconnection time is t 3_off = 900ms, the capacitor terminal voltage is charged to At this time, the average power consumption of the resistor during the t3 period is P R(t3) = 41.748W, the voltage does not meet the requirement that the difference between the final charging voltage and the actual voltage is ≤ 20V, and the fourth charging cycle continues;

[0057] The fourth charging cycle is t4 = 1200ms, and the closing time of the soft start branch is t 4_on =200ms, the soft start branch disconnection time is t 4_off = 1000ms, the capacitor terminal voltage is charged to At this time, the average power consumption of the resistor during the t4 period is P R (t4) = 40.199W, the voltage does not meet the requirement that the difference between the final charging voltage and the actual voltage is ≤ 20V, and the fifth charging cycle is continued;

[0058] The fifth charging cycle is t5 = 1200ms, and the closing time of the soft start branch is t 5_on =200ms, the soft start branch disconnection time is t 5_off = 1000ms, the capacitor terminal voltage is charged to At this time, the average power consumption of the resistor during the t5 period is P R (t5) = 38.856W, the voltage does not meet the requirement that the difference between the final charging voltage and the actual voltage is ≤ 20V, and the sixth charging cycle is continued;

[0059] The sixth charging cycle is t6 = 1220ms, and the closing time of the soft start branch is t 6_on =220ms, the soft start branch disconnection time is t 6_off = 1000ms, the capacitor terminal voltage is charged to At this time, the average power consumption of the resistor during the t6 period is P R (t6) = 38.531W, the voltage does not meet the requirement that the difference between the final charging voltage and the actual voltage is ≤ 20V, and the seventh charging cycle is continued;

[0060] The seventh charging cycle is t7 = 1150ms, and the closing time of the soft start branch is t 7_on =250ms, the soft start branch disconnection time is t 7_off = 900ms, the capacitor terminal voltage is charged to At this time, the average power consumption of the resistor during the t7 period is P R (t7) = 40.536W, the voltage does not meet the requirement that the difference between the final charging voltage and the actual voltage is ≤ 20V, and the eighth charging cycle is continued;

[0061] The eighth charging cycle is t8 = 1100ms, and the closing time of the soft start branch is t 8_on =300ms, the soft start branch disconnection time is t 8_off = 800ms, the capacitor terminal voltage is charged to At this time, the average power consumption of the resistor during the t8 period is P R(t8) = 41.946W, the voltage does not meet the requirement that the difference between the final charging voltage and the actual voltage is ≤ 20V, and the ninth charging cycle is continued;

[0062] The ninth charging cycle is t9 = 1100ms, and the closing time of the soft start branch is t 9_on =400ms, the soft start branch disconnection time is t 9_off =700ms, the capacitor terminal voltage is charged to At this time, the average power consumption of the resistor during the t9 period is P R (t9) = 42.387W, the voltage does not meet the requirement that the difference between the final charging voltage and the actual voltage is ≤ 20V, and the tenth charging cycle is continued;

[0063] The tenth charging cycle is t 10 =1100ms, the closing time of the soft start branch is t 10_on =600ms, the soft start branch disconnection time is t 10_off = 500ms, the capacitor terminal voltage is charged to At this time, the resistance t 10 The average power consumption during the cycle is P R (t 10 )=41.325W, the voltage satisfies the final charge voltage and the actual voltage difference ≤20V, close the main circuit switch, detect after a delay period of Δt, the DC port voltage is detected within the Δt time without exceeding the voltage difference fluctuation, disconnect the soft start branch switch, and the soft start stage with large capacitive load is completed.

[0064] In the above, by detecting the DC port voltage and switching the AC side soft start branch at high frequency, after repeated charging cycles, when the DC port voltage reaches an appropriate value, the AC side main circuit relay is closed to achieve the effect of using a small resistance to carry a large capacitive load. The soft start branch will work at the maximum power point during the entire charging cycle, reducing the size and cost of the soft start branch and realizing the engineering application of capacitive loads.

[0065] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A control method for an AC side high frequency soft start circuit, characterized in that: The soft start circuit includes an AC side power grid, a switch circuit, a DC side capacitive load, an AC / DC converter unit and a controller. The switch circuit includes a main switch K1 and a soft start switch K2 and a soft start resistor R1 connected in parallel therewith. The AC / DC converter unit is arranged between the switch circuit and the capacitive load. The controller regulates the main switch K1 and the soft start switch K2 according to the detected DC side port voltage. The specific process is as follows: 1) The controller is powered; 2) Carry out the first cycle of charging, the charging cycle is t1: 21) The controller sends a command to the switch circuit to close the soft start switch K2 for a closing duration of t 1_on , and then disconnect the soft start switch K2, the disconnection time is t 1_off , t1=t 1_on +t 1_off ; 22) The controller detects whether the DC side port voltage has reached the maximum charging value U max , and whether the pressure difference between the two is less than the set value. If both conditions are met, a command is issued to the switch circuit to close the main switch K1; if one of them is not met, go to step 3); 3) Carry out the second cycle of charging, the charging cycle is t2: 31) The controller sends a command to the switch circuit to close the soft start switch K2 for a closing time of t 2_on , and then disconnect the soft start switch K2, the disconnection time is t 2_off , t2=t 2_on+ t 2_off ; 32) The controller detects whether the DC side port voltage has reached the maximum charging value U max , and whether the voltage difference between the two is less than the set value. If both conditions are met, a command is issued to the switch circuit to close the main switch K1; if one of them is not met, steps 31)-32) are repeated until the DC side port voltage reaches the maximum charging value U max , close the main switch K1 and complete the soft start.

2. The control method of a high-frequency soft-start circuit on the AC side according to claim 1, characterized in that: In step 2), t1 is calculated by formula 1, t 1_on Calculated by formula 2, Among them, U0=0, U c1 is the DC side port voltage detected by the controller at the end of the first cycle charging, τ is the charging time constant, e represents the natural constant; C is the subsequent capacitive load, P1 is the impact power that the soft start resistor can withstand within t1 time, U rms is the AC side grid voltage, In step 3), t2 is calculated by formula 3: t 2_on Calculated by formula 4, Among them, U c2 P2 is the DC side port voltage detected by the controller at the end of the second cycle charging, and P3 is the impact power that the soft start resistor can withstand during the time t2.

3. The control method of the AC side high frequency soft start circuit according to claim 2, characterized in that: The calculation formula of the charging time constant τ is: τ=R×C, R is the resistance value of the soft start resistor R1, and C is the capacitive load of the subsequent stage.

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