Overcurrent suppression method and device for impact load-oriented voltage source converter

Abstract

The invention relates to an impact load-oriented over-current suppression method and device for a voltage source type converter, and the method comprises the following steps: generating a trigger signal of a switching tube locking action when the existence of an overload current caused by an impact load is recognized; sampling the trigger signal, and calculating to obtain a first voltage drop amount according to the captured high level times; generating a second voltage drop based on the inductive current effective value; and taking the sum of the first voltage drop amount and the second voltage drop amount as a total voltage drop amount, generating a modulation wave based on the total voltage drop amount, and further generating a driving pulse signal of a switch tube to suppress the overload current. Compared with the prior art, the over-current protection circuit has the advantages of being reliable in over-current protection, capable of effectively improving the speed of a current-limiting action and the like, can stably output constant current when coping with an impact load, and has good waveform quality.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic control, and in particular to a method and a device for suppressing overcurrent of a voltage source converter facing an impact load. Background Art

[0002] In modern power electronics, voltage source converters are increasingly used, especially in high-power power supply systems, such as uninterruptible power supply systems, distributed power generation systems, etc. Therefore, the stable operation of the load side places high demands on the reliability of the converter in response to overload or short-circuit conditions. When the converter power supply system is connected to an impact load, the response time of the converter overcurrent suppression strategy and the output stability are closely related to the control effect.

[0003] In existing research, dual closed-loop control strategies based on output voltage and current or independent current loop control strategies based on inductor current are often used. For example, Chinese patent application CN107612034A discloses a method for suppressing transient overcurrent of energy storage converters, which samples the inductor current of energy storage converters and suppresses transient overcurrent of energy storage converters under power grid fault conditions through converter port voltage feedforward and variable virtual impedance methods. Although the above two control strategies have certain effects in limiting overload current, the output current waveform is difficult to ensure the stability of converter output, and simultaneously meeting the requirements of rapid overcurrent suppression and output stability poses new challenges to existing overcurrent suppression technologies. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a method and device for overcurrent suppression of a voltage source converter for impact loads, which can achieve reliable overcurrent protection and effectively improve the speed of current limiting action.

[0005] The purpose of the present invention can be achieved by the following technical solutions: A method for suppressing overcurrent of a voltage source converter facing an impact load comprises the following steps: When an overload current caused by an impact load is detected, a trigger signal for the switch tube to lock is generated; Sampling the trigger signal, and calculating a first voltage drop amount according to the number of high level times captured; generating a second voltage drop amount based on the effective value of the inductor current; The sum of the first voltage drop and the second voltage drop is taken as the total voltage drop, a modulation wave is generated based on the total voltage drop, and then a driving pulse signal of the switch tube is generated to suppress the overload current.

[0006] Furthermore, identifying the overload current is specifically as follows: Get the inductor current , determine the inductor current Is it satisfied? If so, an overload current is detected. is the overcurrent protection threshold current.

[0007] Furthermore, the calculation formula of the first voltage drop is: In the formula, is the first voltage drop, To adjust the step size, The number of high level.

[0008] Furthermore, the adjustment step is determined according to the output side reference voltage.

[0009] Furthermore, the second voltage drop is generated by a PI controller based on the effective value of the inductor current.

[0010] Furthermore, the total voltage drop is limited to 0- v p between, v p is the rated output voltage.

[0011] Furthermore, the method further comprises: The trigger signal is continuously sampled, and the number of sampling cycles in which the trigger signal is continuously at a low level is recorded. It is determined that the number of sampling cycles reaches a preset upper limit. If so, a voltage recovery signal is generated to control the first voltage drop to drop to 0, and at the same time control the second voltage drop to increase synchronously to keep the total voltage drop unchanged, thereby achieving constant current control.

[0012] Further, when the first voltage drop amount is controlled to decrease, the voltage drop amount of the first voltage drop amount is: ,in, K re is the voltage recovery step length, is the voltage recovery time, is the first voltage drop.

[0013] Furthermore, the method further comprises: When the impact load begins to recover to a normal operating state, the second voltage drop gradually decreases until it is limited to zero.

[0014] Furthermore, generating a modulation wave based on the total voltage drop is specifically as follows: The total voltage drop is subtracted from the rated output voltage and normalized to obtain the amplitude of the sinusoidal modulation wave and generate the modulation wave.

[0015] The present invention also provides an overcurrent suppression device for a voltage source converter facing an impact load, comprising: A fast voltage suppression loop, for generating a trigger signal for a switch tube lockout action when an overload current caused by an impact load is identified, and for sampling the trigger signal to calculate a first voltage drop amount according to the number of captured high-level times; A current effective value loop, used for generating a second voltage drop amount based on an effective value of an inductor current; The constant voltage loop is used to sum the first voltage drop and the second voltage drop as a total voltage drop, generate a modulation wave based on the total voltage drop, and then generate a driving pulse signal for the switch tube to suppress the overload current.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. When the converter power supply system is connected to an impact load, the present invention quickly identifies the overload current and generates a total voltage drop based on the trigger signal of the switch tube locking action and the effective value of the inductor current. It can respond to different operating conditions to accurately output the voltage drop, achieve reliable overcurrent protection, and effectively improve the speed of the current limiting action.

[0017] 2. The present invention generates a total voltage drop based on the trigger signal of the switch tube locking action and the effective value of the inductor current, performs closed-loop control on the output current, improves the stability of the current when dealing with impact loads, and has a lower harmonic content, avoids false triggering of overcurrent protection action, and further optimizes the waveform quality of the output current.

[0018] 3. In the present invention, when the impact load begins to resume normal operation, the second voltage drop gradually decreases until it is limited to 0, and the output voltage continues to rise until the rated value is fully restored. The output voltage can be restored while maintaining stable power supply, effectively improving the reliability of the converter power supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is an example of a control block diagram of a method for suppressing overcurrent of a voltage source converter according to an embodiment of the present invention; Figure 2 Schematic diagram of the topological structure of a T-type three-level inverter used in an embodiment of the present invention; Figure 3 Flow chart of a method for suppressing overcurrent of a voltage source converter according to an embodiment of the present invention; Figure 4 The waveforms of the a-phase output voltage and the three-phase output current in different control stages in the embodiment of the present invention; Figure 5 Graph 1 is a THD analysis result of the output voltage of phase A during the constant current control stage in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0021] Example 1 This embodiment provides a method for overcurrent suppression of a voltage source converter for impact loads. When the impact load is applied, the method should quickly suppress the overload current by driving the lockout, and stabilize the output constant current by limiting the output voltage rating. This method can reliably achieve overcurrent suppression while improving the speed of the current limiting action.

[0022] The voltage source converter used in this embodiment is a T-type three-level inverter, and its topology is as follows: Figure 2 As shown, the DC bus capacitor is connected to the inverter, and the AC end is connected to the motor load through the LC filter. In this embodiment, the inverter adopts a T-type midpoint clamp topology structure, including 12 switch tubes, 2 DC bus capacitors and an LC filter.

[0023] The above overcurrent suppression method controls the output voltage and current by the output voltage drop. In the overall control process, the system operating conditions can be divided into three stages according to the circuit output and the operating status of the load: the voltage reduction control stage, the constant current control stage, and the load startup stage. Figure 2 and Figure 3 As shown, the overcurrent suppression method includes the following steps: Step S1: Setting the threshold current of overcurrent protection After the impact load is applied, the voltage reduction control stage is entered. The inductor current is detected based on the threshold current to identify whether there is an overload current caused by the impact load. If so, the EMB (emergency break) braking trigger signal is output, that is, the trigger signal for the switch tube locking action: in, i Lx is the sampled inductor current. When the EMB trigger signal outputs a high level, the IGBT is blocked and the inductor current i Lx The instantaneous value is limited to a safe range.

[0024] In this embodiment, the overload current is judged by a hardware comparison circuit. In this embodiment, the output voltage is quickly suppressed according to the state of the EMB trigger signal. When the MCU captures the high level of the EMB trigger signal, the first voltage drop is calculated according to the number of high levels captured. , that is, the calculation formula of the first voltage drop is: In the formula, is the first voltage drop, To adjust the step size, The number of high level. The setting of mainly depends on the requirement for the rapidity of current limiting action. The larger its value, the faster the response speed, but the corresponding control accuracy will be lost. In different embodiments, it needs to be adjusted according to different output side reference voltages to achieve more flexible control. In this embodiment, it is taken as .

[0025] Step S2: Calculate the effective value of the inductor current I rms , generating a second voltage drop v 2. In this embodiment, the PI controller is used to realize the effective value of the inductor current. I rms and the current effective value loop reference value I ref Subtract the error err (k) is then sent to the PI controller to obtain the output v 2: Then calculate the total voltage drop in the step-down control stage v 3: Based on the total voltage drop, a modulation wave is generated, and then a driving pulse signal of the switch tube is generated to suppress overload current. and the second voltage drop v The superposition of 2 can make up for the lack of control accuracy based on a single voltage control signal and improve control reliability.

[0026] It should be noted that in order to achieve the output voltage recovery to the rated value when the load starts, a limit link should be set. v 3Limited to 0- v p between, v p is the rated output voltage.

[0027] Step S3, set the output voltage recovery link, enter the constant current control stage, the purpose of which is: after realizing current protection by rapid voltage reduction, restore the output voltage to the rated value when the load returns to normal working conditions. Continuously sample the trigger signal, record the number of sampling cycles in which the trigger signal is continuously at a low level, and judge that the number of sampling cycles reaches the preset upper limit. If so, generate a voltage recovery signal, control the first voltage drop to drop to 0, and control the second voltage drop to increase to keep the total voltage drop unchanged, so as to realize constant current control.

[0028] Specifically, the voltage recovery signal Determined by the state of the EMB trigger signal: The number of sampling cycles during which the EMB trigger signal remains at a low level is stored in K sum Middle: In each sampling cycle, the EMB trigger signal is judged. If the trigger signal is detected to be low level, the EMB trigger signal is updated. K sum Data: in, The value stored for the next sampling period will be K sum The value and its upper limit K max The value of the voltage recovery signal is generated after comparison: It should be noted that the above K sum Upper limit K max The setting depends on the time when the output voltage recovery link is turned on. In this embodiment, it is set to 100k sampling cycles. In different embodiments, it needs to be flexibly adjusted according to specific working conditions.

[0029] When the voltage recovery signal outputs a high level, the overcurrent suppression strategy enters the constant current control stage, and the first voltage drop is: ,in, K re is the step size of voltage recovery, The duration of voltage recovery. In the constant current control stage, the first voltage drop gradually decreases to 0; the second voltage drop increases synchronously to maintain the total voltage drop unchanged, thus achieving constant current control.

[0030] Step S4: When the impact load begins to recover to a normal operating state, the load starts to start, and the second voltage drop amount gradually decreases until it is limited to 0.

[0031] During the load startup phase, the impact load begins to recover to normal operating state, and the control enters the voltage recovery mode. At this time, the total voltage drop of the control system output is: As the load speed increases, the back EMF rises, the output current continues to decrease, and the total voltage drop further decreases until it is limited to 0 by the limiter; at the same time, the output voltage continues to rise until it fully recovers to the rated value and the startup is completed.

[0032] Step S5: The total voltage drop obtained in step S2, S3 or S4 is v 3 is input as the input quantity into the SPWM modulation wave generator to generate the modulation wave. The specific steps are as follows: With rated output voltage v p Subtract the total voltage drop v 3. And perform normalization to obtain the modulation wave amplitude K s =( v p - v 3) / v p , generating a sinusoidal modulated wave.

[0033] Step S6: Intersect the above modulated wave with the double triangle carrier wave, and generate a driving pulse signal for the switch tube by comparison.

[0034] The above control strategy can quickly limit the overload current to a safe range after the impact load is applied, ensuring the rapidity of the current limiting action and the good waveform quality of the output current. At the same time, it has the ability to start the load. After the impact load returns to normal operation, the output voltage is quickly restored to the rated value to achieve load starting.

[0035] In order to verify the effectiveness of the above control method, this embodiment provides a specific embodiment, and its main parameters are as follows: DC voltage at the input side of the converter V; Rated voltage of converter output side (effective value) V; Switching frequency kHz; Inverter output side impact load power setting kW; Normal operating power setting of the load on the output side of the converter kW; Current protection threshold setting A; Fast voltage suppression loop step-down V; Voltage recovery link flag ; Fast voltage suppression loop voltage recovery coefficient ; Current RMS loop reference value A; Current RMS loop proportionality coefficient ; Current RMS loop integral coefficient .

[0036] Output side a phase output voltage With three-phase output current , , The waveforms at different stages of the control strategy are as follows: Figure 4 As shown, the THD analysis results of the a-phase output voltage are as follows Figure 5 shown.

[0037] Depend on Figure 4 It can be seen that in the initial state, the load connected to the converter power supply system operates under normal conditions. At 0.2 seconds, the impact load is cut in and enters the voltage reduction control stage. The system detects the overload current and quickly suppresses it, and completes the overcurrent suppression action within half a fundamental wave cycle. After completing the overcurrent suppression action, it enters the constant current control stage. The inductor current is stably controlled at the set rated value and gradually transitions to the independent current effective value loop control; at 1 second, the impact load resumes normal operating conditions and enters the load startup stage. The output voltage completely recovers to the rated value within 1 fundamental wave cycle, and the overload suppression and load startup process is reliably completed, thereby verifying the effectiveness of the control method of the present invention. Figure 5 This is the harmonic analysis result of the output voltage of phase a of this embodiment. It can be seen from the figure that in the constant current control stage, the harmonic content THD is 2.94%, which effectively proves the waveform quality under the control of the overcurrent suppression strategy.

[0038] Example 2 This embodiment provides a voltage source converter overcurrent suppression device for impact loads, such as Figure 1 As shown, including: A fast voltage suppression loop is used to generate a trigger signal for the switch tube to lock when an overload current caused by an impact load is identified, and to sample the trigger signal, and to calculate the first voltage drop according to the number of captured high-level times. The fast voltage suppression loop includes a hardware comparison circuit and an EMB (emergency break) control circuit. A current effective value loop, used for generating a second voltage drop amount based on an effective value of an inductor current; The constant voltage loop is used to sum the first voltage drop and the second voltage drop as a total voltage drop, generate a modulation wave based on the total voltage drop, and then generate a driving pulse signal for the switch tube to suppress overload current.

[0039] The above-mentioned fast voltage suppression loop, current effective value loop and constant voltage loop are all provided with limiters to limit the output to 0- v p between.

[0040] The overcurrent suppression process based on the above-mentioned overcurrent suppression device is as follows Figure 3 As shown, including: Step S1, in the overall control process, the fast voltage suppression loop and the current effective value loop both control the output voltage and current by the output voltage drop, and the system operating conditions are divided into three stages according to the output of the control loop and the operating status of the load: the voltage reduction control stage, the constant current control stage, and the load startup stage.

[0041] Set the threshold current for overcurrent protection After the impact load is applied, it enters the step-down control stage, uses the hardware comparison circuit to detect the inductor current, and outputs the EMB braking trigger signal.

[0042] In this embodiment, the output voltage is quickly suppressed according to the state of the EMB trigger signal. When the MCU captures the high level of the EMB trigger signal, the output of the voltage loop is adjusted immediately to control the output of the voltage loop in the next switching cycle to: in, v 1(k) is the output of the current voltage suppression loop, v 1(k+1) is the output of the voltage suppression loop in the next cycle. is the step size of each adjustment.

[0043] Step S2: Calculate the effective value of the inductor current I rms , and compare it with the current effective value loop reference value I ref Subtract the error err (k) is then sent to the PI controller to obtain the output of the current effective value loop v 2: According to the total number of braking triggers m, the total voltage drop in the voltage reduction control stage is calculated. v 3: It should be noted that in order to achieve the output voltage recovery to the rated value when the load starts, a limit link should be set. v3Limited to 0- v p between, v p Determined by the output of the constant pressure loop.

[0044] Step S3: Collecting voltage recovery signal When the voltage recovery signal outputs a high level, the overcurrent suppression strategy enters the constant current control stage. At this time, the voltage drop output by the voltage suppression loop is: ,in, K re is the step size of voltage recovery, is the duration of voltage recovery. In the constant current control stage, the output of the voltage suppression loop gradually decreases to 0; the error input of the PI loop in the current effective value loop increases, and the output increases synchronously, thereby maintaining the total voltage drop unchanged and achieving constant current control.

[0045] Step S4: To ensure that the inverter power supply system can meet the requirement of output voltage recovery to rated value when the load is started, there are two working modes for different loads: 1. Voltage suppression mode: to deal with impact load, the control strategy accurately outputs the voltage drop. , maintain constant current operation; 2. Voltage recovery mode: to deal with the load under normal operating conditions, the voltage loop is completely closed, and the control system is controlled by an independent inductor current effective value loop. As the load returns to normal conditions, the output of the current effective value loop gradually decreases and is eventually controlled to 0 by the limiting link, so that the output voltage gradually returns to the rated value.

[0046] During the load startup phase, the impact load begins to recover to normal operating state, and the control enters the voltage recovery mode. At this time, the total voltage drop of the control system output is: As the load speed increases, the back EMF rises, the output current continues to decrease, and the total voltage drop further decreases until it is limited to 0 by the limiter; at the same time, the output voltage continues to rise until it fully recovers to the rated value and the startup is completed.

[0047] At the same time, if Figure 1 As shown, in this embodiment, a constant voltage loop control is provided, the purpose of which is to perform closed-loop control on the effective value of the output voltage after the load enters a normal working condition, so as to avoid output voltage fluctuations caused by the internal resistance of the device.

[0048] Step S5: The total voltage drop v 3 is input as the input quantity into the SPWM modulation wave generator to generate the modulation wave. The specific steps are as follows: With rated output voltage v p Subtract the total voltage drop v3. And perform normalization to obtain the modulation wave amplitude K s =( v p - v 3) / v p , generating a sinusoidal modulated wave.

[0049] Step S6: Intersect the above modulated wave with the double triangle carrier wave, and generate a driving pulse signal for the switch tube by comparison.

[0050] The rest is the same as in Example 1.

[0051] It should be noted that the above overcurrent suppression method can be used in voltage source converters, including but not limited to applications in Figure 2 In the topology shown; and the EMB control comes from the switch tube drive locking function of the controller, including but not limited to the controller used in this embodiment.

[0052] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for suppressing overcurrent of a voltage source converter for impact load, characterized in that: The following steps are involved: When an overload current caused by an impact load is identified, a trigger signal for the switch tube to lock out is generated; Sampling the trigger signal, and calculating a first voltage drop amount according to the number of high-level times captured; generating a second voltage drop amount based on the effective value of the inductor current; The sum of the first voltage drop and the second voltage drop is taken as the total voltage drop, a modulation wave is generated based on the total voltage drop, and then a driving pulse signal of the switch tube is generated to suppress the overload current.

2. The overcurrent suppression method for voltage source converter facing impact load according to claim 1, characterized in that: Identifying the overload current is specifically as follows: Get the inductor current , determine the inductor current Is it satisfied? If so, an overload current is detected. is the overcurrent protection threshold current.

3. The overcurrent suppression method for voltage source converter facing impact load according to claim 1, characterized in that: The calculation formula of the first voltage drop is: ， In the formula, is the first voltage drop, To adjust the step size, The adjustment step is determined according to the output side reference voltage.

4. The overcurrent suppression method for voltage source converter facing impact load according to claim 1, characterized in that: The second voltage drop amount is generated by a PI controller based on the effective value of the inductor current.

5. The overcurrent suppression method for voltage source converter facing impact load according to claim 1, characterized in that: The total voltage drop is limited to 0- v p between, v p is the rated output voltage.

6. The overcurrent suppression method for voltage source converter facing impact load according to claim 1, characterized in that: The method further includes: The trigger signal is continuously sampled, and the number of sampling cycles in which the trigger signal is continuously at a low level is recorded. It is determined that the number of sampling cycles reaches a preset upper limit. If so, a voltage recovery signal is generated to control the first voltage drop to drop to 0, and at the same time control the second voltage drop to increase synchronously to keep the total voltage drop unchanged, thereby achieving constant current control.

7. The overcurrent suppression method for voltage source converter facing impact load according to claim 6, characterized in that: When the first voltage drop amount is controlled to decrease, the voltage drop amount of the first voltage drop amount is: ,in, K re is the voltage recovery step length, is the voltage recovery time, is the first voltage drop.

8. The overcurrent suppression method for voltage source converter facing impact load according to claim 1, characterized in that: The method further includes: When the impact load begins to recover to a normal operating state, the second voltage drop gradually decreases until it is limited to zero.

9. The overcurrent suppression method for voltage source converter facing impact load according to claim 1, characterized in that: The specific method for generating the modulation wave based on the total voltage drop is as follows: The total voltage drop is subtracted from the rated output voltage and normalized to obtain the amplitude of the sinusoidal modulation wave to generate the modulation wave.

10. A voltage source converter overcurrent suppression device for impact load, characterized in that: include: A fast voltage suppression loop, for generating a trigger signal for a switch tube lockout action when an overload current caused by an impact load is identified, and for sampling the trigger signal to calculate a first voltage drop amount according to the number of captured high-level times; A current effective value loop, used for generating a second voltage drop amount based on an effective value of an inductor current; The constant voltage loop is used to sum the first voltage drop and the second voltage drop as a total voltage drop, generate a modulation wave based on the total voltage drop, and then generate a driving pulse signal for the switch tube to suppress the overload current.

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