Anti-overcurrent control system and control method for voltage slope starting of power electronic converter

Abstract

The invention discloses an anti-overcurrent control system and control method for voltage slope starting of a power electronic converter, and solves the problems that when an existing power electronic converter with single voltage setting is controlled, inductive current oscillation is too large; however, by adopting the existing method, the difficulty of a control algorithm is increased, the requirement on computing resources is improved, and the debugging work is increased. The method comprises the steps of collecting output voltage of the power electronic converter and inductive current in the power electronic converter; a sampling interval time is set, the difference value between the slope starting voltage of the power electronic converter and the output voltage of the power electronic converter is obtained to serve as the input of a voltage PI outer ring controller, and the output value of the voltage PI outer ring controller is collected; calculating an interception value according to the total voltage slope starting time, the sampling interval time and the slope starting current of the power electronic converter; the input of a current PI inner loop controller is determined; and the current of the current PI inner loop controller is set as a linear rising slope which does not exceed the cut-off value.

Description

Technical Field

[0001] The invention relates to an overcurrent protection method for a power electronic converter, and in particular to an overcurrent protection control system and a control method for a power electronic converter voltage ramp starting. Background Art

[0002] In power electronic converter systems, the dual-loop control strategy including the voltage PI outer loop controller and the current PI inner loop controller is widely used due to its advantages such as high dynamics, current cutoff function, and easy algorithm implementation.

[0003] In the prior art, when controlling a power electronic converter with a single voltage setting, the conventional control steps are as follows:

[0004] ①Run to the set rated ramp starting voltage and adjust the control parameters under full power constant load;

[0005] ② Test sudden loading, sudden unloading and other working conditions according to specification requirements and optimize parameters;

[0006] ③ Test the product status under load starting conditions.

[0007] During the test, the parameters debugged in steps ① and ② are generally not suitable for the ramp soft start condition, resulting in current shock, voltage oscillation, voltage overshoot and other phenomena. Simulation results (see Figure 1 ), the upper left Vout is the output voltage of the power electronic converter; the lower left I_out is the output current of the power electronic converter; the upper right V_Uctrl_Out is the voltage loop output; the lower right I_L is the inductor current of the power electronic converter, and it can be seen that the inductor current oscillates.

[0008] In order to solve the above problems, the following two solutions are generally adopted:

[0009] 1. Use fuzzy PID and expert PID methods. The specific implementation is as follows (see Figure 2 ):

[0010] A limit value of error is defined as Mmax, a relatively large value of error is defined as Mmid, a smaller value of error is defined as Mmin, the output voltage of the power electronic converter is used as voltage feedback, and the ramp starting voltage of the power electronic converter is used as a voltage setting;

[0011] Calculate the difference between the given voltage and the feedback voltage, abs(Verror). When abs(Verror)>Mmax, it means that the absolute value of the error is already very large. Regardless of the error change trend, the controller input should be considered to be at the maximum (or minimum) output to achieve the effect of quickly adjusting the error and reduce the absolute value of the error at the fastest speed. At this point, it is equivalent to implementing open-loop control;

[0012] When Mmid>abs(Verror)>Mmin, it means that the absolute value of the error is at a medium level and a general control effect is implemented;

[0013] When Mmin>abs(Verror), it means that the difference abs(Verror) is very small. At this time, integration is added to reduce the static error.

[0014] The above method determines the degree of deviation and uses different adjustment strengths to meet the requirements of the system, which will increase the difficulty of the control algorithm and increase the requirements for computing resources.

[0015] 2. Use different control parameters for different working conditions.

[0016] When debugging the voltage ramp start of the power electronic converter, the control loop parameters are re-adjusted according to the measurement data of the voltage slope, current impact and other conditions of the power electronic converter to avoid problems such as overcurrent and voltage oscillation. This parameter is used when the voltage ramp starts the power electronic converter, and another set of parameters is used after constant voltage, which will increase the debugging work. Summary of the invention

[0017] The purpose of the present invention is to solve the problem that when the existing power electronic converter is started with a given voltage ramp, the inductor current may oscillate too much, the current impact may trigger an overcurrent fault shutdown, or the difficulty of the control algorithm may be increased, the requirements for computing equipment may be increased, or the debugging work may be increased. The present invention provides an overcurrent prevention control system and control method for voltage ramp starting of a power electronic converter.

[0018] In order to achieve the above object, the present invention adopts the following technical solution:

[0019] An overcurrent prevention control system for voltage ramp startup of a power electronic converter, which is special in that it includes a data acquisition unit, a voltage PI outer loop control unit, a current limit unit and a current PI inner loop control unit;

[0020] The data acquisition unit is used to collect the output voltage of the power electronic converter and the inductor current in the power electronic converter; the two output ends of the data acquisition unit are respectively connected to the first input end of the voltage PI outer loop control unit and the first input end of the current PI inner loop control unit;

[0021] The second input end of the voltage PI outer loop control unit is connected to the given ramp starting voltage of the power electronic converter, and is used to perform voltage PI control on the difference between the given ramp starting voltage of the power electronic converter and the output voltage of the power electronic converter according to the set sampling interval time to obtain the voltage PI outer loop control output value, and the output end of the voltage PI outer loop control unit is connected to the second input end of the current PI inner loop control unit;

[0022] The current limiting unit is used to calculate the interception value according to the total voltage ramp start time, the sampling interval time and the given power electronic converter ramp start current; the output end of the current limiting unit is connected to the third input end of the current PI inner loop control unit;

[0023] The current PI inner loop control unit is used to take the smaller value of the voltage PI outer loop control output value and the interception value as the current setting, and perform current PI control on the difference between the current setting and the inductor current in the power electronic converter. The output end of the current PI inner loop output control unit is used to connect to the wave modulation unit of the power electronic converter.

[0024] Further, in the current limiting unit, the intercept value I_ is calculated by the following formula: Ref_Ramp :

[0025] I_ Ref_Ramp =I limit ·(K num / K max );

[0026] Among them, I limit t num The ramp starting current of the power electronic converter at this moment;

[0027] K max is the total number of sampling times, t step is the sampling interval, t total is the total voltage ramp start time, Indicates rounding down x;

[0028] K num t num The number of samples at a time, t num is the current time when the voltage ramp starts, t num ≤t total .

[0029] Furthermore, the voltage PI outer loop control unit includes a first subtractor and a voltage PI outer loop controller, the first input end of the first subtractor is connected to the given ramp starting voltage of the power electronic converter, the second input end is connected to the voltage output end of the data acquisition unit, and the voltage output end outputs the output voltage of the power electronic converter, the output end of the first subtractor is connected to the input end of the voltage PI outer loop controller, and the output end of the voltage PI outer loop controller is connected to the second input end of the current PI inner loop control unit.

[0030] Further, the current PI inner loop control unit includes a selection comparator, a second subtractor and a current PI inner loop controller, wherein the selection comparator is used to compare and select a smaller value;

[0031] The first input end of the selection comparator is connected to the output end of the voltage PI outer loop control unit, the second input end is connected to the output end of the current limiting unit, the output end is connected to the first input end of the second subtractor, the second input end of the second subtractor is connected to the current output end of the data acquisition unit, and the current output end outputs the inductor current in the power electronic converter, the output end of the second subtractor is connected to the input end of the current PI inner loop controller, and the output end of the current PI inner loop controller is used to connect to the wave modulation unit of the power electronic converter.

[0032] Furthermore, the sampling time interval is 10 to 100 us.

[0033] A method for preventing overcurrent during voltage ramp startup of a power electronic converter is based on a method for preventing overcurrent during voltage ramp startup of a power electronic converter. The method is characterized in that the method comprises the following steps:

[0034] S1. Define the starting time of the voltage ramp start of the power electronic converter as time 0, give the ramp start voltage and ramp start current of the power electronic converter at each time during the voltage ramp start, and set the sampling interval time;

[0035] S2, recording the actual time of the voltage ramp start of the power electronic converter, and collecting the output voltage of the power electronic converter and the inductor current in the power electronic converter through a data acquisition unit;

[0036] S3, according to the set sampling interval time, the voltage PI control is performed on the difference between the given power electronic converter ramp starting voltage and the power electronic converter output voltage to obtain the voltage PI outer loop control output value;

[0037] S4, calculating the interception value according to the total voltage ramp start time, the sampling interval time and the given power electronic converter ramp start current;

[0038] S5, comparing the output value of the voltage PI outer loop controller and the interception value, selecting the smaller value as the current setting, performing current PI control through the difference between the current setting and the inductor current in the power electronic converter, obtaining the current PI inner loop control output value, and inputting the current PI inner loop control output value into the wave modulation unit of the power electronic converter to realize the overcurrent prevention control of the voltage ramp start;

[0039] S6, judging whether the actual voltage ramp start time of the power electronic converter reaches the total voltage ramp start time, and if so, completing the voltage ramp start;

[0040] If the total voltage ramp start time has not been reached, the process returns to S2.

[0041] Furthermore, S4 is specifically:

[0042] Assume the total voltage ramp start time is t total , the sampling interval is t step , t num Ramp start current I limit , calculate the total number of sampling times K max for:

[0043]

[0044] Indicates rounding down x;

[0045] At the current moment, the voltage ramp start time is t num The sampling times K at this moment num for:

[0046]

[0047] Among them, t num ≤t total ;

[0048] t num Moment cut-off value I_ Ref_Ramp The calculation formula is:

[0049] I_ Ref_Ramp =I limit ·(K num / K max ).

[0050] Furthermore, the sampling interval described in S1 is set to 10 to 100 us.

[0051] Beneficial effects of the present invention:

[0052] 1. The present invention discloses an overcurrent prevention control system and control method for voltage ramp starting of a power electronic converter. In the voltage ramp starting of a power electronic converter controlled by a voltage PI outer loop controller and a current PI inner loop controller, a cutoff value is set for the current setting of the power electronic converter, so that the current setting of the current PI inner loop controller is a linear rising slope that does not exceed the cutoff value.

[0053] 2. The present invention provides an overcurrent protection control system and control method for voltage ramp starting of a power electronic converter, which solves the problem of overcurrent fault shutdown caused by current impact when a power electronic converter with a single voltage setting starts with a voltage ramp; at the same time, it avoids the problem of large fluctuations in output voltage caused by incompatibility of control parameters; and can reduce the complexity of the control algorithm and the requirements for computer computing resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a schematic diagram of simulation results in the background technology of the present invention;

[0055] Among them, the upper left Vout is the output voltage of the power electronic converter; the lower left I_out is the output current of the power electronic converter; the upper right V_Uctrl_Out is the output of the voltage PI outer loop controller; the lower right I_L is the inner loop current;

[0056] Figure 2 It is a structural principle diagram of the fuzzy PID and expert PID method used in the background technology of the present invention;

[0057] Figure 3 It is a structural principle diagram of an embodiment of an overcurrent prevention control method for voltage ramp startup of a power electronic converter according to the present invention;

[0058] Figure 4 It is a simulation data curve diagram of an overcurrent prevention control method embodiment of a power electronic converter voltage ramp start-up according to the present invention;

[0059] Figure 5 It is a simulation waveform diagram in an embodiment of an overcurrent prevention control method for voltage ramp startup of a power electronic converter of the present invention;

[0060] Among them, the upper left Vout is the output voltage of the power electronic converter; the lower left I_out is the output current of the power electronic converter; the upper right V_Uctrl_Out is the output of the voltage PI outer loop controller; and the lower right I_L is the inductor current of the power electronic converter. DETAILED DESCRIPTION

[0061] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] In this embodiment, an overcurrent prevention control system for voltage ramp startup of a power electronic converter includes a data acquisition unit, a voltage PI outer loop control unit, a current limiting unit, and a current PI inner loop control unit;

[0063] A data acquisition unit is used to collect the output voltage of the power electronic converter and the inductor current in the power electronic converter; two output ends of the data acquisition unit are respectively connected to the first input end of the voltage PI outer loop control unit and the first input end of the current PI inner loop control unit;

[0064] The second input end of the voltage PI outer loop control unit is connected to the given ramp starting voltage of the power electronic converter, and is used to perform voltage PI control on the difference between the given ramp starting voltage of the power electronic converter and the output voltage of the power electronic converter according to the set sampling interval time, which is 20us in this embodiment, to obtain the voltage PI outer loop control output value, and the output end of the voltage PI outer loop control unit is connected to the second input end of the current PI inner loop control unit;

[0065] The voltage PI outer loop control unit includes a first subtractor and a voltage PI outer loop controller. The first input end of the first subtractor is connected to the given ramp starting voltage of the power electronic converter, the second input end is connected to the voltage output end of the data acquisition unit, and the voltage output end outputs the output voltage of the power electronic converter. The output end of the first subtractor is connected to the input end of the voltage PI outer loop controller, and the output end of the voltage PI outer loop controller is connected to the second input end of the current PI inner loop control unit.

[0066] The current limiting unit is used to calculate the interception value according to the total voltage ramp starting time, the sampling interval time and the given power electronic converter ramp starting current; the output end of the current limiting unit is connected to the third input end of the current PI inner loop control unit;

[0067] The cutoff value I_ Ref_Ramp :

[0068] I_ Ref_Ramp =I limit ·(K num / K max );

[0069] Among them, I limit t numThe ramp starting current of the power electronic converter at this moment;

[0070] K max is the total number of sampling times, t step is the sampling interval, t total is the total voltage ramp start time, Indicates rounding down x;

[0071] K num t num The number of samples at a time, t num is the current time when the voltage ramp starts, t num ≤t total .

[0072] The current PI inner loop control unit is used to take the smaller value of the voltage PI outer loop control output value and the interception value as the current setting, and perform current PI control on the difference between the current setting and the inductor current in the power electronic converter. The output end of the current PI inner loop output control unit is used to connect to the wave modulation unit of the power electronic converter.

[0073] The current PI inner loop control unit comprises a selection comparator, a second subtractor and a current PI inner loop controller, wherein the selection comparator is used for comparing and selecting a smaller value;

[0074] The first input end of the comparator is selected to be connected to the output end of the voltage PI outer loop control unit, the second input end is connected to the output end of the current limiting unit, the output end is connected to the first input end of the second subtractor, the second input end of the second subtractor is connected to the current output end of the data acquisition unit, and the current output end outputs the inductor current in the power electronic converter, the output end of the second subtractor is connected to the input end of the current PI inner loop controller, and the output end of the current PI inner loop controller is used to connect to the wave modulation unit of the power electronic converter.

[0075] In this embodiment, a method for preventing overcurrent during voltage ramp startup of a power electronic converter is provided. Figure 3 As shown, the voltage ramp starting of the power electronic converter controlled by the voltage PI outer loop controller and the current PI inner loop controller includes the following steps:

[0076] S1. Define the starting time of the voltage ramp start of the power electronic converter as time 0, give the ramp start voltage and ramp start current of the power electronic converter at each time during the voltage ramp start, and set the sampling interval to 20us;

[0077] S2, recording the actual time of the voltage ramp start of the power electronic converter, collecting the output voltage Vout of the power electronic converter and the inductor current I_out in the power electronic converter at a certain moment;

[0078] S3, according to the set sampling interval time, the slope starting voltage of the given power electronic converter is subtracted from the output voltage Vout of the power electronic converter at the corresponding moment, and the voltage PI control is performed according to the difference to obtain the output value V_Uctrl_Out of the voltage PI outer loop controller;

[0079] S4, calculating the interception value according to the total voltage ramp start time, the sampling interval time and the given ramp start current of the power electronic converter; specifically:

[0080] Assume the total voltage ramp start time is t total , the sampling interval is t step , t num Ramp start current I limit , calculate the total number of sampling times K max for:

[0081]

[0082] Indicates rounding down x;

[0083] At the current moment, the voltage ramp start time is t num The sampling times K at this moment num for:

[0084]

[0085] Among them, t num ≤t total ;

[0086] t num Moment cut-off value I_ Ref_Ramp The calculation formula is:

[0087] I_ Ref_Ramp =I limit ·(K num / K max ).

[0088] S5, comparing the output value of the voltage PI outer loop controller and the interception value, selecting the smaller value as the current setting, performing current PI control through the difference between the current setting and the inductor current in the power electronic converter, obtaining the current PI inner loop control output value, and inputting the current PI inner loop control output value into the wave modulation unit of the power electronic converter to realize the overcurrent prevention control of the voltage ramp start;

[0089] S6, judging whether the actual voltage ramp start time of the power electronic converter reaches the total voltage ramp start time, and if so, completing the voltage ramp start;

[0090] If the total voltage ramp start time has not been reached, the process returns to S2.

[0091] The method in this embodiment is used for simulation. The rated voltage of the power electronic converter used when stable is 710V, and the rated current when stable is 21.5A; the total time of voltage ramp start is 80ms, and the sampling time interval is 20us. The serial number of the data used and the corresponding sampling time, ramp start voltage, and ramp start current are shown in Table 1. Figure 4 shown.

[0092] Table 1

[0093]

[0094] The simulation effect diagram obtained in this embodiment is as follows Figure 5 As shown, according to Figure 5 It can be seen that the output voltage Vout in the upper left corner rises steadily without oscillation; the inductor current of the I_L power electronic converter in the lower right corner rises steadily without oscillation. It can be seen that the method of the present invention solves the problem of large-scale output voltage oscillation caused by incompatible control parameters and can also reduce the problem of current impact.

[0095] It can be seen from this embodiment and the simulation results that the sampling algorithm in the overcurrent protection control system and control method of the voltage ramp start of the power electronic converter of the present invention is simple and easy to implement, has low requirements on the computing equipment, and can effectively reduce the debugging time.

[0096] The above description is only a specific embodiment of the present invention, and a comparison of the effects of the specific embodiments and the related comparative examples, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An overcurrent prevention control system for voltage ramp startup of a power electronic converter, characterized in that: It includes a data acquisition unit, a voltage PI outer loop control unit, a current limiting unit and a current PI inner loop control unit; The data acquisition unit is used to collect the output voltage of the power electronic converter and the inductor current in the power electronic converter; the two output ends of the data acquisition unit are respectively connected to the first input end of the voltage PI outer loop control unit and the first input end of the current PI inner loop control unit; The second input end of the voltage PI outer loop control unit is connected to the given ramp starting voltage of the power electronic converter, and is used to perform voltage PI control on the difference between the ramp starting voltage of the power electronic converter and the output voltage of the power electronic converter according to the set sampling interval time to obtain the voltage PI outer loop control output value, and the output end of the voltage PI outer loop control unit is connected to the second input end of the current PI inner loop control unit; The current limiting unit is used to calculate the interception value according to the total voltage ramp start time, the sampling interval time and the given power electronic converter ramp start current; the output end of the current limiting unit is connected to the third input end of the current PI inner loop control unit; The current PI inner loop control unit is used to take the smaller value of the voltage PI outer loop control output value and the interception value as the current setting, and perform current PI control on the difference between the current setting and the inductor current in the power electronic converter. The output end of the current PI inner loop output control unit is used to connect to the wave modulation unit of the power electronic converter.

2. The overcurrent prevention control system for voltage ramp startup of a power electronic converter according to claim 1, characterized in that: In the current limiting unit, the intercept value I_ is calculated by the following formula: Ref_Ramp : I_ Ref_Ramp =I limit ·(K num / K max ); Among them, I limit t num The ramp starting current of the power electronic converter at this moment; K max is the total number of sampling times, t step is the sampling interval, t total is the total voltage ramp start time, Indicates rounding down x; K num t num The number of samples at a time, t num is the current time when the voltage ramp starts, t num ≤t total .

3. The overcurrent prevention control system for voltage ramp startup of a power electronic converter according to claim 1, characterized in that: The voltage PI outer loop control unit includes a first subtractor and a voltage PI outer loop controller, wherein the first input end of the first subtractor is connected to the given ramp starting voltage of the power electronic converter, the second input end is connected to the voltage output end of the data acquisition unit, and the voltage output end outputs the output voltage of the power electronic converter, the output end of the first subtractor is connected to the input end of the voltage PI outer loop controller, and the output end of the voltage PI outer loop controller is connected to the second input end of the current PI inner loop control unit.

4. The overcurrent prevention control system for voltage ramp startup of a power electronic converter according to claim 1, characterized in that: The current PI inner loop control unit includes a selection comparator, a second subtractor and a current PI inner loop controller, wherein the selection comparator is used to compare and select a smaller value; a first input end of the selection comparator is connected to the output end of the voltage PI outer loop control unit, a second input end is connected to the output end of the current limiting unit, and the output end is connected to the first input end of the second subtractor, a second input end of the second subtractor is connected to the current output end of the data acquisition unit, and the current output end outputs the inductor current in the power electronic converter, an output end of the second subtractor is connected to the input end of the current PI inner loop controller, and an output end of the current PI inner loop controller is used to connect to the wave modulation unit of the power electronic converter.

5. The overcurrent prevention control system for voltage ramp startup of a power electronic converter according to claim 1, characterized in that: The sampling time interval is 10 to 100 us.

6. A method for preventing overcurrent during voltage ramp startup of a power electronic converter, based on the method for preventing overcurrent during voltage ramp startup of a power electronic converter according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Define the starting time of the voltage ramp start of the power electronic converter as time 0, give the ramp start voltage and ramp start current of the power electronic converter at each time during the voltage ramp start, and set the sampling interval time; S2, recording the actual time of the voltage ramp start of the power electronic converter, and collecting the output voltage of the power electronic converter and the inductor current in the power electronic converter through a data acquisition unit; S3, according to the set sampling interval time, the voltage PI control is performed on the difference between the given power electronic converter ramp starting voltage and the power electronic converter output voltage to obtain the voltage PI outer loop control output value; S4, calculating the interception value according to the total voltage ramp start time, the sampling interval time and the given power electronic converter ramp start current; S5, comparing the output value of the voltage PI outer loop controller and the interception value, selecting the smaller value as the current setting, performing current PI control through the difference between the current setting and the inductor current in the power electronic converter, obtaining the current PI inner loop control output value, and inputting the current PI inner loop control output value into the wave modulation unit of the power electronic converter to realize the overcurrent prevention control of the voltage ramp start; S6, judging whether the actual voltage ramp start time of the power electronic converter reaches the total voltage ramp start time, and if so, completing the voltage ramp start; If the total voltage ramp start time has not been reached, the process returns to S2.

7. The overcurrent prevention control method for voltage ramp starting of a power electronic converter according to claim 6, characterized in that: S4 is specifically: Assume the total voltage ramp start time is t total , the sampling interval is t step , t num Ramp start current I limit , calculate the total number of sampling times K max for: Indicates rounding down x; At the current moment, the voltage ramp start time is t num The sampling times K at this moment num for: Among them, t num ≤t total ; t num Moment cut-off value I_ Ref_Ramp The calculation formula is: I_ Ref_Ramp =I limit ·(K num / K max )。 8. The overcurrent prevention control method for voltage ramp startup of a power electronic converter according to claim 6, characterized in that: The sampling interval described in S1 is set to 10 to 100 us.

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