Method for detecting output current of frequency converter and frequency converter

Abstract

The application discloses a detection method of output current of a frequency converter and the frequency converter. The detection method of output current of the frequency converter comprises the following steps: obtaining current fluctuation time when a semiconductor switch is turned on; setting minimum turn-on time of the semiconductor switch to be greater than the current fluctuation time; and setting a current detection time point in the turn-on time of the semiconductor switch to be after the current fluctuation time. The detection method of output current of the frequency converter and the frequency converter can reduce the error between a detected current and an actual current in the case of long-distance wiring.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of frequency converters, and particularly relates to a detection method for output current of a frequency converter and the frequency converter. BACKGROUND

[0002] According to different user purposes, sometimes the wiring of the frequency converter can exceed 200 meters, and the detected current value can sometimes fluctuate greatly, and the difference between the detected current and the actual current can sometimes become very large, which can result in the occurrence of overcurrent or overload. SUMMARY

[0003] The inventor has found that when the length of the output wiring is increased, the capacitance and inductance of the wiring are increased, which results in great fluctuation of the current. For small-capacity frequency converters, the influence of the fluctuation is great on the current detection method, especially in the high-frequency field, and the detected current can be greater than the actual current.

[0004] As shown in FIG. 1, in the case of a normal wiring of 10 m, the voltage across the voltage dividing resistor does not fluctuate, and thus no false detection occurs. However, when the wiring distance is long (for example, 500 m) and the working frequency is below 40 Hz, although there is current fluctuation, the pulse width is large, and thus the current detection is not affected. However, when the wiring distance is long (for example, 500 m) and the working frequency is above 40 Hz, the pulse width is small, and thus the current fluctuation greatly affects the current detection. Figure 1 Further analysis shows that, as shown in FIG. 2, this is because there is an inductive component (inductance, capacitance) of the wiring, and thus a leakage current is generated. As can be seen from the calculation formula i = 2ΠF X C X V of the leakage current, the longer the wiring distance, the greater the leakage current. The leakage current flows from the frequency converter end, and the leakage current is added to the detected current, so that the detected current is also correspondingly increased. The current fluctuation caused by the wiring inductance will make the detected current greater than the actual current in the case of voltage dividing current detection, and thus false detection occurs. The voltage dividing current detection is to detect the current across the voltage dividing resistor in the on interval of the N-side IGBT. Therefore, the fluctuation phenomenon in the on interval of the N-side IGBT must occur.

[0005] Figure 2 In view of the above analysis, an object of the present application is to provide a detection method for output current of a frequency converter and the frequency converter, which can reduce the error between the detected current and the actual current in the case of long wiring.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] A detection method for output current of a frequency converter, comprising the following steps:

[0008] A detection method for output current of a frequency converter, comprising the following steps:​

[0009] acquiring a current fluctuation time at the time of turning on the semiconductor switch;

[0010] setting a minimum turn-on time of the semiconductor switch to be greater than the current fluctuation time;

[0011] setting a current detection time point in the turn-on time of the semiconductor switch to be after the current fluctuation time.

[0012] As a preferred embodiment, the detection method comprises the following steps:

[0013] determining an initial turn-on time of the semiconductor switch according to the length of the wiring;

[0014] determining an actual current fluctuation time in the initial turn-on time of the semiconductor switch;

[0015] setting a minimum turn-on time of the semiconductor switch to be greater than the actual current fluctuation time;

[0016] setting a current detection time point in the turn-on time of the semiconductor switch to be after the actual current fluctuation time.

[0017] As a preferred embodiment, the step of determining the initial turn-on time of the semiconductor switch comprises:

[0018] determining an initial current fluctuation time according to the length of the wiring;

[0019] setting the initial turn-on time of the semiconductor switch to be greater than the initial current fluctuation time.

[0020] As a preferred embodiment, the initial turn-on time of the semiconductor switch is the initial current fluctuation time plus a first predetermined time; the first predetermined time is taken from the range of 2 microseconds to 10 microseconds.

[0021] As a preferred embodiment, the initial current fluctuation time comprises: a theoretical current fluctuation time calculated by using a corresponding relation formula of the length of the wiring and the current fluctuation time, or an empirical value of the current fluctuation time determined according to the length of the wiring, or a pre-stored current fluctuation time determined according to pre-stored different lengths of the wiring corresponding to the current fluctuation time.

[0022] As a preferred embodiment, the initial turn-on time of the semiconductor switch is determined according to pre-stored different lengths of the wiring corresponding to the turn-on time of the semiconductor switch.

[0023] As a preferred embodiment, the step of determining the actual current fluctuation time comprises:

[0024] determining an initial current detection time point after the initial current fluctuation time in the initial turn-on time of the semiconductor switching element;

[0025] sampling forward from the initial current detection time point at a predetermined interval time until an initial current stable time point is obtained, and taking the time before the initial current stable time point as the actual current fluctuation time.

[0026] As a preferred embodiment, the initial current detection time point is located in the interval [the last time point of the initial current fluctuation time, the last time point of the initial turn-on time of the semiconductor switching element).

[0027] As a preferred embodiment, the initial current detection time point is the last time point of the initial turn-on time of the semiconductor switching element after the initial current fluctuation time plus a second predetermined time, wherein 0≤ the second predetermined time < the first predetermined time.

[0028] As a preferred embodiment, the predetermined interval time is 1-3 microseconds.

[0029] As a preferred embodiment, the u-phase current value sampled at the initial current detection time point is Iu(0), the u-phase current value sampled at the nth current detection time point is Iu(n), and the last current detection time point at which the difference between Iu(n) and Iu(0) is less than a predetermined value is taken as the initial current stable time point.

[0030] As a preferred embodiment, the step of determining the minimum turn-on time of the semiconductor switching element includes: the minimum turn-on time of the semiconductor switching element is the actual current fluctuation time plus a third predetermined time; and the third predetermined time is taken from the range 2-10 microseconds.

[0031] As a preferred embodiment, the step of setting the current detection time point includes: setting the current detection time point at a time point after 1 / 2 of the turn-on time of the semiconductor switching element plus a predetermined time; and the predetermined time is calculated according to the formula: the predetermined time is equal to one-half of the minimum turn-on time of the semiconductor switching element minus a predetermined adjustment value.

[0032] As a preferred embodiment, the predetermined adjustment value is less than the third predetermined time.

[0033] As a preferred embodiment, when the number of current detections required to obtain the initial current stable time point is greater than or equal to a predetermined detection number, the minimum turn-on time of the semiconductor switching element is set to be greater than the actual current fluctuation time.

[0034] As a preferred implementation, the detection method further comprises: setting the minimum turn-on time of the semiconductor switch to be greater than the initial current fluctuation time when the number of current detection times required to obtain the initial current steady time point is less than the predetermined detection times; and setting the current detection time point in the turn-on time of the semiconductor switch to be after the initial current fluctuation time.

[0035] As a preferred implementation, the detection method comprises the following steps:

[0036] sending a test pulse; setting the turn-on time of the semiconductor switch in the test pulse to be greater than the initial current fluctuation time; and setting the turn-on time of the semiconductor switch in each cycle in the test pulse to be equal;

[0037] sending a working pulse; and setting the minimum turn-on time of the semiconductor switch in the working pulse to be greater than the actual current fluctuation time.

[0038] As a preferred implementation, the detection method comprises the following steps:

[0039] determining the current fluctuation time when the semiconductor switch is turned on according to the length of the wiring;

[0040] setting the minimum turn-on time of the semiconductor switch to be greater than the current fluctuation time;

[0041] setting the current detection time point in the turn-on time of the semiconductor switch to be after the current fluctuation time.

[0042] As a preferred implementation, the semiconductor switch comprises an N-side IGBT and / or a P-side IGBT; and the current detection is performed by AD conversion sampling of U-phase current.

[0043] A frequency converter comprises a processor and a memory for storing processor-executable instructions; the instructions are executed by the processor to implement the steps of the detection method of the output current of the frequency converter according to any one of the above embodiments.

[0044] Advantages:

[0045] The detection method of the output current of the frequency converter provided by the embodiment can reduce the influence of the current fluctuation generated when the semiconductor switch is turned on on the current detection by expanding the minimum turn-on time of the semiconductor switch and delaying the current detection time point, and thus the detection method can reduce the error between the detected current and the actual current and improve the accuracy of the detected current in the case of long-distance wiring.

[0046] The particular embodiments of the application will be described in relation to the enclosed drawings and the following description, as examples of the principles of the application that can be employed in various and numerous embodiments. It is to be understood that there is no intent to limit the application to the particular embodiments described in relation to the drawings and the description below.

[0047] Features described and / or illustrated with respect to one embodiment can be used in one or more other embodiments in the same or similar manner, in combination with or in place of other features disclosed with respect to an embodiment, or in combination with or in place of features not specifically disclosed with respect to an embodiment.

[0048] It should be emphasized that the term comprises / comprising, when used in this specification, is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. BRIEF DESCRIPTION OF DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description only illustrate some of the embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0050] Figure 1 is a schematic diagram of current detection by voltage division in different cases;

[0051] Figure 2 is a schematic diagram of current detection in the case of long-distance wiring;

[0052] Figure 3 is a flow chart of the method for detecting the output current of the frequency converter provided by an embodiment of the present application;

[0053] Figure 4 is a schematic diagram of the start timing of Figure 3

[0054] Figure 5 is a schematic diagram of the minimum on-time adjustment of Figure 4 DETAILED DESCRIPTION

[0055] In order for those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings of the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should be within the scope of protection of the present application.

[0056] ​​Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0057] Referring to Figure 3 One embodiment of the present application provides a method for detecting output current of a frequency converter, comprising the following steps:

[0058] S100, obtaining a current fluctuation time when a semiconductor switching element is turned on;

[0059] S200, setting a minimum turn-on time of the semiconductor switching element to be greater than the current fluctuation time;

[0060] S300, setting a current detection time point in the turn-on time of the semiconductor switching element to be after the current fluctuation time.

[0061] The semiconductor switching element realizes the change of frequency and amplitude of power supply through on-off control. The turn-on time of the semiconductor switching element can include the current fluctuation time and a current stabilization time. The current stabilization time is after the current fluctuation time. The semiconductor switching element can include a transistor. In the embodiment, the semiconductor switching element includes an N-side IGBT and / or a P-side IGBT. Figure 2 As shown in the figure, the frequency converter includes P-side IGBTs (PU, PV, PW) and N-side IGBTs (NU, NV, NW). The P-side IGBTs and the N-side IGBTs cooperate to realize the frequency conversion control of power supply. Each N-side IGBT is connected in series with a voltage dividing resistor, and the voltage dividing resistor is used for voltage dividing current detection, and the currents are Iu, Iv and Iw respectively. The current detection is performed as AD conversion sampling of U-phase current. That is, the current detection time point is the AD conversion current detection time point in the embodiment.

[0062] The method for detecting output current of the frequency converter provided in the embodiment can reduce the influence of current fluctuation generated when turned on on current detection by expanding the minimum turn-on time of the semiconductor switching element and delaying the current detection time point. Therefore, the method for detecting output current of the frequency converter provided in the embodiment can reduce the error between the detected current and the actual current in the case of long-distance wiring, and improve the accuracy of the detected current.

[0063] In the embodiment, the current fluctuation time is the actual current fluctuation time. Specifically, the step S100 can comprise the steps of: S101, determining the initial switching-on time of the semiconductor switch according to the length of the wiring; and S120, determining the actual current fluctuation time in the initial switching-on time of the semiconductor switch.

[0064] Correspondingly, the detection method comprises the steps of:

[0065] S110, determining the initial switching-on time of the semiconductor switch according to the length of the wiring;

[0066] S120, determining the actual current fluctuation time in the initial switching-on time of the semiconductor switch;

[0067] S201, setting the minimum switching-on time of the semiconductor switch to be greater than the actual current fluctuation time;

[0068] S301, setting the current detection time point in the switching-on time of the semiconductor switch to be after the actual current fluctuation time.

[0069] Further, the step (S101) of determining the initial switching-on time of the semiconductor switch comprises: S111, determining the initial current fluctuation time according to the length of the wiring; and S112, setting the initial switching-on time of the semiconductor switch to be greater than the initial current fluctuation time.

[0070] In the embodiment, since the minimum switching-on time of the semiconductor switch is limited, the desired short pulse cannot be outputted, and the waveform of the output current is distorted. In order to reduce the distortion of the waveform and make the waveform of the output current as close to the desired waveform as possible, the initial switching-on time of the semiconductor switch can be slightly greater than the initial current fluctuation time.

[0071] Specifically, the initial switching-on time of the semiconductor switch is the initial current fluctuation time plus a first predetermined time. The first predetermined time is taken from the range of 2 microseconds to 10 microseconds. The initial current fluctuation time comprises a theoretical current fluctuation time calculated by using a corresponding relationship formula of the length of the wiring and the current fluctuation time, or an empirical value of the current fluctuation time determined according to the length of the wiring, or a pre-stored current fluctuation time determined according to the pre-stored current fluctuation time corresponding to different lengths of the wiring. Generally, the initial current fluctuation time is greater than the actual current fluctuation time, and thus the last time point of the initial current fluctuation time is generally within the current stable time of the initial switching-on time of the semiconductor switch.

[0072] Of course, the initial turn-on time of the semiconductor switch can also be determined directly by the length of the wiring, for example, according to the pre-stored semiconductor switch turn-on time corresponding to different wiring lengths to determine the initial turn-on time of the semiconductor switch. The corresponding data information of the wiring length and the semiconductor switch turn-on time can be stored in the memory of the frequency converter, which can be stored in the form of a table, or the corresponding data can be stored in the form of a database. For example, as shown in the following table:

[0073] Wiring length / m Semiconductor switch on time / ps A A’ B B’ C C’

[0074] In the case of determining the wiring length as Am, the processor can directly determine the semiconductor switch turn-on time as A' μs according to the corresponding information of the above table pre-stored in the memory, and then determine A' μs as the initial turn-on time of the semiconductor switch.

[0075] For different wiring lengths, the setting method and the inductance of the wiring are different. The current detection and the turn-on time of the IGBT need to be adjusted each time, which is troublesome. Therefore, the frequency converter of the embodiment can first send a test pulse after power-on. In the test pulse, the turn-on time of the semiconductor switch in each period is equal. The actual current fluctuation time is obtained by using the test pulse. Specifically, the turn-on time of the semiconductor switch in the test pulse is set to be greater than the initial current fluctuation time. Steps S111, S112 and S120 are performed in the process of sending the test pulse. The actual current fluctuation time in the initial turn-on time of the semiconductor switch can be determined by the test pulse.

[0076] Then, the frequency converter sends a working pulse. The minimum turn-on time of the semiconductor switch in the working pulse is set to be greater than the actual current fluctuation time. The current detection time point in the turn-on time of the semiconductor switch in the working pulse is set after the actual current fluctuation time. The motor is driven by using the working pulse. At this time, the current detected by using the voltage division detection method avoids the current fluctuation time, so that the gap between the detected current and the true current value is reduced, and the current detection is more accurate.

[0077] The detection method of the output current of the frequency converter of the embodiment obtains the actual current fluctuation time by using the test pulse, sets the working pulse based on this, so that the minimum turn-on time of the semiconductor switch in the working pulse is greater than the actual current fluctuation time, and the current detection time point avoids the actual current fluctuation time, and the current detection (current detection sampling) is performed in the current stable time, so as to obtain the detected current close to the true current value.

[0078] In the embodiment, the actual current fluctuation time is determined according to the following steps: S121, determining an initial current detection time point after the initial current fluctuation time in the initial turn-on time of the semiconductor switch; S122, sampling forward from the initial current detection time point according to a predetermined interval time until an initial current stable time point is obtained, and taking the time before the initial current stable time point as the actual current fluctuation time. It can be understood that the time after the initial current stable time point can also be taken as the actual current stable time, as an alternative to or included in step S122. In order to reduce the distortion of the waveform of the actual output current, the predetermined interval time is 1-3 microseconds.

[0079] Further, the initial current detection time point is located in the interval [the last time point of the initial current fluctuation time, the last time point of the initial turn-on time of the semiconductor switch). That is, the initial current detection time point can be any time point after the initial current fluctuation time (excluding the last time point of the initial turn-on time of the semiconductor switch). Alternatively, the initial current detection time point is the last time point of the initial turn-on time of the semiconductor switch plus a second predetermined time, where 0≤the second predetermined time

[0080] In the embodiment, in order to obtain the actual current fluctuation time (which can also be regarded as determining the actual current stable time), the u-phase current value sampled at the initial current detection time point is Iu(0), and the u-phase current value sampled at the nth current detection time point is Iu(n). The last current detection time point at which the absolute value of the difference between Iu(n) and Iu(0) is less than a predetermined value is taken as the initial current stable time point. Correspondingly, the first current detection time point at which the absolute value of the difference between Iu(n) and Iu(0) is greater than the predetermined value can also be taken as the last current fluctuation time point.

[0081] In the embodiment, in order to ensure the reliability of the results obtained by sampling and ensure that the subsequent adjustment of the minimum turn-on time (ON amplitude) of the semiconductor is more reliable, when the number of current detections required to obtain the initial current stable time point is greater than or equal to a predetermined detection number, the minimum turn-on time of the semiconductor switch is set to be greater than the actual current fluctuation time. Generally speaking, the number of current detections (which can also be understood as the number of samplings) in the current stable time is more than 5, which can ensure that the time period is the current stable time, and the current detection (AD conversion sampling) performed in the time period is closer to the true current value.

[0082] Accordingly, in this detection method, when the number of current detections required to obtain the initial current stabilization time is less than the predetermined number of detections, the minimum turn-on time of the semiconductor switch is set to be greater than the initial current fluctuation time. Consequently, the current detection time point within the semiconductor switch turn-on time is set after the initial current fluctuation time. Furthermore, in this case, the frequency converter can also output a long-distance wiring abnormality warning signal.

[0083] Furthermore, the current detection time point is set as follows: the current detection time point is set after half the semiconductor switch's on-time, delayed by a fourth predetermined time (the fourth predetermined time can be understood as a delayed detection time). The fourth predetermined time is calculated according to the following formula: the fourth predetermined time equals half the semiconductor switch's on-time minus a predetermined adjustment value. The predetermined adjustment value is less than the third predetermined time.

[0084] In this embodiment, the step of determining the minimum turn-on time of the semiconductor switch after determining the actual current fluctuation time includes: adding a third predetermined time to the actual current fluctuation time as the minimum turn-on time of the semiconductor switch. That is, the minimum turn-on time of the semiconductor switch is the actual current fluctuation time plus the third predetermined time. The third predetermined time is taken from the range of 2 microseconds to 10 microseconds.

[0085] The first, second, and third pre-set times can be the same or different; this application does not impose any particular limitation. In practical applications, the magnitude of the first, second, and third pre-set times can be determined according to specific needs. For example, the first pre-set time can be 2 microseconds, the second pre-set time can be 1 microsecond, and the third pre-set time can be 4 microseconds.

[0086] The following is in conjunction with the appendix Figure 4 Appendix Figure 5 The method for detecting the inverter output current in this embodiment is described in detail to better understand the present invention.

[0087] Adjustments are implemented during the first operation of the inverter after power is connected. The inverter first enters the initial charging sequence and detects a load short circuit. When the load short circuit is detected, the carrier frequency trough is inserted (corresponding to time points ① and ③), and the PWM operation cycle is inserted at time points ②, ④, ⑥, and ⑧. Specifically, the carrier period is set to about 5kHz (interval times = 1). The insertion of the carrier frequency trough and the insertion of the PWM operation cycle are the same as the existing processing method, and will not be repeated here. The U-phase current AD value, denoted as Iu[0]···Iu

[37] , is obtained at time points such as ⑤ and ⑦.

[0088] For example, in the case of a wiring length of 500 m, the fluctuation duration of the phase current is about 35 μs, and therefore the phase current at the position of 40 μs should be in a stable state. Based on this, the turn-on time of the (P, N side) IGBT is set to 45 μs. The time point of the first detection of the phase current (U phase) (initial current detection time point) is 40 μs. At this time, the u phase current value obtained by the initial current detection is stored as Iu[0]. The delay time of the initial current detection time point is 17.5 μs (i.e., the delay time is equal to the initial current detection time point minus half of the IGBT turn-on time, 40 - 45 / 2 = 17.5 μs).

[0089] In the next cycle (second PWM cycle), the turn-on time of the P, N side IGBT is maintained at 45 μs, and the predetermined interval time of the adjacent two current detection time points is set to 1 μs. Thus, when the second detection of the phase current (U phase) is performed, the second current detection time point is set to 39 μs, and at this time, the u phase current value obtained by the second current detection is stored as Iu[1]. The delay time of the second current detection time point is 39 - 45 / 2 = 16.5 μs. Then, it is determined whether the second current detection time point is the initial current stable time point based on the absolute value of the difference between Iu[1] and Iu[0]. Specifically, when |Iu[1] - Iu[0]| ≤ P3-01 (P3-01 is a predetermined value for the determination, i.e., a fluctuation amplitude threshold value), it is determined that the second current detection time point is in the current stable time, and the count (CNT1 = 1).

[0090] Next, in the next cycle, the turn-on time of the P, N side IGBT is maintained at 45 μs, and when the third detection of the phase current (U phase) is performed, the third current detection time point is set to 35 μs, and at this time, the u phase current value obtained by the third current detection is stored as Iu[2]. In the third current detection, |Iu[2] - Iu[0]| ≤ P3-01, and at this time, it is determined that the third current detection time point is in the current stable time, and the count (CNT1 = 2).

[0091] Thus, up to the thirteenth detection of the phase current (U phase), the thirteenth current detection time point is set to 28 μs, and at this time, the u phase current value obtained by the thirteenth current detection is stored as Iu

[12] . The delay time of the thirteenth current detection time point is 28 - 45 / 2 = 5.5 μs. In the thirteenth current detection, |Iu

[12] - Iu[0]| ≤ P3-01, and at this time, it is determined that the thirteenth current detection time point is in the current stable time, and the count (CNT1 = 12).

[0092] In the next cycle, the turn-on time of the P, N-side IGBTs continues to be 45 μs. When the 14th detection current is detected, the 14th current detection time point is set at 27 μs, at which time the u-phase current value obtained by the 14th current detection is saved as Iu

[13] . Here, the delay time of the 14th current detection time point is 27-45 / 2=4.5 μs. Correspondingly, in this current detection, it is found that |Iu

[13] -Iu[0]|>P3-01, at which time it is determined that the 14th current detection time point is in the current fluctuation time, the counting is stopped, i.e., no counting (CNT1=13). The automatic adjustment function ends, and the test pulse is sent.

[0093] It can be seen that the 13th current detection time point (28 μs) is the initial current stabilization time point, and the 14th current detection time point is the last current fluctuation time point. In this embodiment, the time before the 13th current detection time point is regarded as the actual current fluctuation time, and the detection current value obtained at the 13th current detection time point has a small error and is close to the true current value.

[0094] After the actual current fluctuation time is determined, the minimum turn-on time of the P, N-side IGBTs is adjusted for the working pulse. First, it is determined whether the current stabilization time reaches a certain length. In the case where it is determined that the current stabilization time meets a certain length, it can be determined that there is indeed a certain length of current stabilization time in the turn-on time, indicating that the obtained current detection result is relatively reliable and true. Specifically, whether the current stabilization time reaches a certain length can be determined by whether the number of current detections is greater than a predetermined number, and then whether the detection result is usable is determined.

[0095] Further, when CNT1≥P3-02 (the predetermined detection number, i.e., the predetermined current detection number), it is indicated that the current stabilization time meets a certain length, the detection data is reliable, and then the minimum turn-on time of the P, N-side IGBTs is set to 40 μs-CNT1 (12)+P3-03 (P3-03 is the third predetermined time, which can also be understood as the output current adjustment amplitude), and the current detection time point can be set at any time point after 28 μs.

[0096] In this embodiment, T0=1 / 2*L1+(1 / 2*L2-△t0), L2=T1+△t1,△t0≤△t1,△t1>0. Here, T0 is the current detection time point, L1 is the IGBT turn-on time, L2 is the minimum IGBT turn-on time,△t0 is a predetermined adjustment value, T1 is the initial current stabilization time point, and△t1 is the third predetermined time.

[0097] When CNT1 < P3-02 (predetermined number of detection times), it is indicated that the current stabilization time is too short, and thus it can be considered that a long distance wiring abnormality (Long Distance Alarm: LD) is detected. In this case, the minimum turn-on time of the P and N side IGBTs is set to the initial 45 μs, and the delay time of the current detection is directly set to the initial 17.5 μs.

[0098] In another embodiment, the detection method of this embodiment can be preferably used in the case where a long distance wiring abnormality is detected. Of course, in order to shorten the automatic adjustment time, the detection method of the frequency converter output current of this embodiment can also be directly used, and thus it is not necessary to send the detection pulse. In this embodiment, the current fluctuation time can be the theoretical current fluctuation time or the empirical current fluctuation time. The current fluctuation time is specifically determined by the wiring length. Specifically, the detection method of the frequency converter output current includes the following steps:

[0099] S100', determining the current fluctuation time at the turn-on time of the semiconductor switching element according to the wiring length;

[0100] S200', setting the minimum turn-on time of the semiconductor switching element to be greater than the current fluctuation time;

[0101] S300', setting the current detection time point in the turn-on time of the semiconductor switching element to be after the current fluctuation time.

[0102] One embodiment of the present application also provides a frequency converter, including a processor and a memory for storing processor executable instructions; the instructions are executed by the processor to implement the steps of the detection method of the frequency converter output current according to any one of the above embodiments.

[0103] Any numerical values cited in this document are inclusive of all values from lower to upper values inclusive of the lower and upper values in increments of one unit, there being at least two units of difference between any lower value and any higher value. By way of example, if a value for a quantity of a component or a process variable (e.g. temperature, pressure, time, etc.) is stated as being from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, it is intended to state explicitly that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32, etc. are also explicitly stated in the specification. For values less than 1, it is appropriate to consider that a unit is 0.0001, 0.001, 0.01, 0.1. These are merely examples of what is intended to be explicitly stated, and it is considered that all possible combinations of values stated between the lowest value and the highest value are explicitly stated in a similar manner in the specification.

[0104] All ranges are inclusive of the endpoints and of all numbers between the endpoints unless otherwise indicated. "About" or "approximately," as applied to any numerical range, means that the exact value can be somewhat outside the stated range and still fall within the range of equivalency. Thus, "about 20 to 30" is intended to cover "about 20 to about 30," at least including the specified endpoints.

[0105] It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and many applications besides the examples provided herein will be apparent to those of skill in the art upon reading the above description. The scope of the teachings should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are incorporated by reference for the purpose of the present disclosure. Any portion of the subject matter described herein can be presented in a manner substantially identical to the subject matter described in the foregoing application(s) and to equivalents thereof, even though that subject matter is not expressly described in the foregoing application(s).

Claims

1. A method of detecting an output current of a frequency converter, characterized by The method comprises the following steps: The step of obtaining the current fluctuation time when the semiconductor switch is turned on comprises: determining the initial turn-on time of the semiconductor switch according to the length of the wiring, specifically comprising determining the initial current fluctuation time according to the length of the wiring, setting the initial turn-on time of the semiconductor switch to be greater than the initial current fluctuation time, or determining the initial turn-on time of the semiconductor switch according to the pre-stored semiconductor switch turn-on time corresponding to different wiring lengths; and determining the actual current fluctuation time in the initial turn-on time of the semiconductor switch. The step of setting the minimum turn-on time of the semiconductor switch to be greater than the current fluctuation time comprises: setting the minimum turn-on time of the semiconductor switch to be greater than the actual current fluctuation time. The step of setting the current detection time point in the turn-on time of the semiconductor switch after the current fluctuation time comprises: setting the current detection time point in the turn-on time of the semiconductor switch after the actual current fluctuation time.

2. The detection method of claim 1, wherein, The initial turn-on time of the semiconductor switch is the initial current fluctuation time plus a first predetermined time; the first predetermined time is taken from the range of 2 microseconds to 10 microseconds.

3. The detection method as described in claim 1, characterized in that, The initial current fluctuation time comprises: a theoretical current fluctuation time calculated by using a corresponding relationship formula of the length of the wiring and the current fluctuation time, or an empirical value of the current fluctuation time determined according to the length of the wiring, or a pre-stored current fluctuation time determined according to the pre-stored current fluctuation time corresponding to different wiring lengths.

4. The detection method of claim 2, wherein, The step of determining the actual current fluctuation time comprises: An initial current detection time point is determined after the initial current fluctuation time in the initial turn-on time of the semiconductor switch; An initial current stable time point is obtained by sampling forward from the initial current detection time point at a predetermined interval time, and the time before the initial current stable time point is taken as the actual current fluctuation time.

5. The detection method of claim 4, wherein, The initial current detection time point is located in the interval [the last time point of the initial current fluctuation time, the last time point of the initial turn-on time of the semiconductor switch).

6. The detection method as described in claim 4, characterized in that, The initial current detection time point is the last time point of the initial turn-on time of the semiconductor switch plus a second predetermined time, wherein 0≤the second predetermined time<the first predetermined time.

7. The detection method as described in claim 4, characterized in that, The predetermined interval time is 1 microsecond to 3 microseconds.

8. The detection method as described in claim 4, characterized in that, The u-phase current value sampled at the initial current detection time point is Iu(0), the u-phase current value sampled at the subsequent nth current detection time point is Iu(n), and the last current detection time point satisfying the absolute value of the difference between Iu(n) and Iu(0) being less than a predetermined value is taken as the initial current stable time point.

9. The method of claim 1, wherein, The step of determining the minimum turn-on time of the semiconductor switch comprises: the minimum turn-on time of the semiconductor switch is the actual current fluctuation time plus a third predetermined time; and the third predetermined time is taken from the range of 2 microseconds to 10 microseconds.

10. The detection method of claim 9, wherein, The step of setting the current detection time point comprises setting the current detection time point at a fourth predetermined time after a 1 / 2 time point of the semiconductor switch on time; the fourth predetermined time is calculated according to the following formula: the fourth predetermined time equals to one half of the minimum semiconductor switch on time minus a predetermined adjustment value.

11. The detection method of claim 10, wherein, The predetermined adjustment value is not more than the third predetermined time.

12. The method of claim 8, wherein the detecting is performed by a method selected from the group consisting of mass spectrometry, nuclear magnetic resonance, and chromatography. When the number of current detections required to obtain the initial current steady time point is greater than or equal to a predetermined detection number, the minimum semiconductor switch on time is set to be greater than the actual current fluctuation time.

13. The detection method of claim 12, wherein, Further comprising: When the number of current detections required to obtain the initial current steady time point is less than the predetermined detection number, the minimum semiconductor switch on time is set to be greater than the initial current fluctuation time; correspondingly, the current detection time point in the semiconductor switch on time is set after the initial current fluctuation time.

14. The method of claim 1, wherein, The detection method comprises the following steps: sending a test pulse; setting the semiconductor switch on time in the test pulse to be greater than the initial current fluctuation time; in the test pulse, the semiconductor switch on time in each cycle is equal; sending a working pulse; setting the minimum semiconductor switch on time in the working pulse to be greater than the actual current fluctuation time.

15. The method of claim 1 to 14, wherein: The semiconductor switch comprises N-side IGBT and / or P-side IGBT; the current detection is performed by AD conversion sampling of U-phase current.

16. A frequency converter, characterized in that The inverter comprises a processor and a memory for storing processor executable instructions; the instructions are executed by the processor to implement the steps of the detection method of the inverter output current according to any one of claims 1 to 15.

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