Control method and circuit of frequency converter, frequency converter and electric equipment

Abstract

The invention provides a frequency converter control method and circuit, a frequency converter and electric equipment, and the method comprises the steps: taking an input voltage of a three-phase rectification circuit in the frequency converter, judging whether the maximum value of the input voltage of the three-phase rectification circuit collected in a current period is in a first preset range or not, and judging whether the minimum value of the input voltage is in a second preset range or not; and when the maximum value is not within the first preset range and / or the minimum value is not within the second preset range, calculating a compensation coefficient, and adjusting the modulation ratio of the frequency converter based on the compensation coefficient so as to reduce the fluctuation amplitude of the output voltage of the frequency converter. And frequent over-voltage and under-voltage protection shutdown of frequency converter electric equipment caused by large input voltage fluctuation of the frequency converter is avoided.

Description

Technical Field

[0001] The present invention relates to the field of electrical control technologies, and particularly to a control method, a circuit, an inverter, and an electrical device for an inverter. Background Art

[0002] Due to unstable power supply voltage in engineering power consumption, in order to protect large centrifugal units from problems, overvoltage protection, undervoltage protection and other measures are usually adopted to protect the units, that is, the operation of the units is stopped when there are large fluctuations in the continuous voltage. If the grid voltage is unstable, the units will frequently stop for protection, which will affect the user side and the user experience.

[0003] Therefore, an inverter is usually used to control the voltage regulation. The existing inverter control technologies usually rely on a fixed input voltage range. When the input voltage fluctuates greatly, the stability and quality of the output voltage will be affected, causing the electrical device connected to the inverter to frequently stop due to overvoltage protection. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a control method, a circuit, an inverter, and an electrical device for an inverter to prevent the electrical device from frequently stopping due to overvoltage protection caused by voltage fluctuations.

[0005] To achieve the above object, embodiments of the present invention provide the following technical solutions:

[0006] A control method for an inverter, including:

[0007] Obtaining the input voltage of a three-phase rectifier circuit in the inverter;

[0008] Judging whether the maximum value of the input voltage in the current period is within a first preset range;

[0009] Judging whether the minimum value of the input voltage in the current period is within a second preset range;

[0010] When the maximum value of the input voltage is not within the first preset range and / or the minimum value of the input voltage is not within the second preset range, calculating a compensation coefficient;

[0011] Adjusting the output modulation ratio of the inverter based on the compensation coefficient.

[0012] Optionally, in the above control method for an inverter, it further includes:

[0013] Obtaining the bus voltage of an electrical device connected to the output end of the inverter;

[0014] Performing PI regulation based on the comparison result between the bus voltage and a reference voltage;

[0015] Obtain a compensation coefficient that matches the output result of the PI regulation, and control the output modulation ratio of the frequency converter based on the compensation coefficient.

[0016] Optionally, in the above control method of the frequency converter, when the maximum value of the input voltage is not within the first preset range or the minimum value of the input voltage is not within the second preset range, calculating the compensation coefficient includes:

[0017] When the maximum value of the input voltage is not within the first preset range, calculate the difference between the maximum value of the input voltage and the first reference value, and denote it as the first difference;

[0018] When the minimum value of the input voltage is not within the second preset range, calculate the difference between the minimum value of the input voltage and the second reference value, and denote it as the second difference;

[0019] When it is detected that the first difference and / or the second difference is generated, obtain a compensation coefficient that matches the generated difference based on a preset mapping table.

[0020] A control circuit of a frequency converter includes:

[0021] An input voltage detection circuit for obtaining the input voltage of the three-phase rectifier circuit in the frequency converter;

[0022] A voltage change analysis circuit for determining whether the maximum value of the input voltage is within a first preset range in the current cycle; determining whether the minimum value of the input voltage is within a second preset range;

[0023] A compensation coefficient calculation circuit for calculating a compensation coefficient when the maximum value of the input voltage is not within the first preset range or the minimum value of the input voltage is not within the second preset range;

[0024] A modulation circuit for adjusting its own output modulation ratio based on the compensation coefficient.

[0025] Optionally, in the above control circuit of the frequency converter, the input voltage detection circuit includes:

[0026] A first comparator and the peripheral circuit of the first comparator;

[0027] The non-inverting input terminal of the first comparator is used to obtain the voltage of the S-phase line and the reference voltage in the input voltage of the three-phase rectifier circuit;

[0028] The inverting input terminal of the first comparator is used to obtain the voltage of the R-phase line in the input voltage of the three-phase rectifier circuit.

[0029] Optionally, in the above control circuit of the frequency converter, the peripheral circuit in the input voltage detection circuit includes:

[0030] A first resistor, the first end of the first resistor is connected to the R-phase line of the input voltage of the three-phase rectifier circuit, and the second end of the first resistor is connected to the inverting input terminal of the first comparator;

[0031] A second resistor, the first end of the second resistor is connected to the S-phase line of the input voltage of the three-phase rectifier circuit, and the second end of the first resistor is connected to the non-inverting input terminal of the first comparator;

[0032] A third resistor, the first end of the third resistor obtains the reference voltage, and the second end of the third resistor is connected to the non-inverting input terminal of the first comparator;

[0033] A fourth resistor, the first end of the fourth resistor is connected to the inverting input terminal of the first comparator, and the second end of the fourth resistor is connected to the output terminal of the first comparator;

[0034] A fifth resistor, the first end of the fifth resistor is connected to the output terminal of the first comparator, and the second end of the fifth resistor serves as the output terminal of the input voltage detection circuit;

[0035] A first capacitor, the first end of the first capacitor is connected to the inverting input terminal of the first comparator, and the second end of the first capacitor is grounded;

[0036] A second capacitor, the first end of the second capacitor is connected to the non-inverting input terminal of the first comparator, and the second end of the second capacitor is grounded;

[0037] A third capacitor, the third capacitor is connected in parallel with the third resistor;

[0038] A fourth capacitor, the fourth capacitor is connected in parallel with the fourth resistor;

[0039] A fifth capacitor, the first end of the fifth capacitor is connected to the second end of the fifth resistor, and the second end of the fifth capacitor is grounded.

[0040] Optionally, in the control circuit of the above frequency converter, it further includes:

[0041] A bus voltage detection circuit for obtaining the bus voltage of the electrical equipment connected to the output end of the frequency converter;

[0042] The compensation coefficient calculation circuit is further configured to perform PI regulation based on the comparison result of the bus voltage and the reference voltage; obtain a compensation coefficient matching the output result of the PI regulation, and control the output modulation ratio of the frequency converter based on the compensation coefficient.

[0043] Optionally, in the control circuit of the above frequency converter, the bus voltage detection circuit includes:

[0044] A second comparator, a third comparator, and a peripheral circuit;

[0045] The inverting input terminal of the second comparator is connected to the N-phase line in the bus of the electrical equipment, and the non-inverting input terminal of the second comparator is connected to the P-phase line in the bus of the electrical equipment;

[0046] The inverting input terminal of the third comparator is connected to the output terminal of the third comparator, and the non-inverting input terminal of the third comparator is connected to the output terminal of the second comparator.

[0047] Optionally, in the control circuit of the above-mentioned frequency converter, the peripheral circuit in the bus voltage detection circuit includes:

[0048] A sixth resistor, the first end of the sixth resistor is connected to the N-phase line in the bus of the electrical equipment, and the second end of the sixth resistor is connected to the inverting input terminal of the second comparator;

[0049] A seventh resistor, the first end of the seventh resistor is connected to the P-phase line in the bus of the electrical equipment, and the second end of the seventh resistor is connected to the non-inverting input terminal of the second comparator;

[0050] An eighth resistor, the first end of the eighth resistor is connected to the non-inverting input terminal of the second comparator, and the second end of the eighth resistor is grounded;

[0051] A ninth resistor, the first end of the ninth resistor is connected to the inverting input terminal of the second comparator, and the second end of the ninth resistor is connected to the output terminal of the second comparator;

[0052] A tenth resistor, the first end of the tenth resistor is connected to the output terminal of the third comparator, and the second end of the tenth resistor serves as the output terminal of the bus voltage detection circuit;

[0053] A sixth capacitor, the sixth capacitor is connected in parallel with the eighth resistor;

[0054] A seventh capacitor, the seventh capacitor is connected in parallel with the ninth resistor.

[0055] A frequency converter includes the control circuit of the frequency converter described in any one of the above.

[0056] An electrical equipment includes the above-mentioned frequency converter.

[0057] Based on the above technical solutions, for the above solutions provided in the embodiments of the present invention, the input voltage of the three-phase rectifier circuit in the frequency converter is taken, and it is determined whether the maximum value of the input voltage of the three-phase rectifier circuit collected in the current period is within the first preset range and whether the minimum value of the input voltage is within the second preset range. When the maximum value is not within the first preset range and / or the minimum value is not within the second preset range, a compensation coefficient is calculated, and the modulation ratio of the frequency converter is adjusted based on the compensation coefficient to reduce the fluctuation amplitude of the output voltage of the frequency converter, and to avoid frequent over-voltage and under-voltage protection shutdown of the electrical equipment powered by the frequency converter due to large fluctuations in the input voltage of the frequency converter. Description of the Drawings

[0058] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0059] Figure 1 Flow schematic diagram of the control method of the frequency converter disclosed in the embodiments of the present application;

[0060] Figure 2 Schematic diagram of the preset voltage range configuration method disclosed in the embodiments of the present application;

[0061] Figure 3 Flow schematic diagram of the control method of the frequency converter disclosed in another embodiment of the present application;

[0062] Figure 4 Block diagram of the bus voltage closed-loop control;

[0063] Figure 5 Schematic diagram of the structure of the control circuit of the frequency converter disclosed in the embodiments of the present application;

[0064] Figure 6 Schematic diagram of the structure of the input voltage acquisition circuit;

[0065] Figure 7 Schematic diagram of the structure of the bus voltage acquisition circuit;

[0066] Figure 8 Output voltage waveform diagram of the frequency converter when the grid voltage is 310VAC;

[0067] Figure 9 Output voltage waveform diagram of the frequency converter when the grid voltage is 515VAC. Detailed Embodiments

[0068] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0069] To solve the problem in the prior art, a control method for an inverter is proposed. By collecting the input voltage of the inverter, once the change in the input voltage is detected, the compensation coefficient will be immediately calculated, and the output modulation ratio of the inverter will be adjusted to reduce the influence of the input voltage fluctuation on the output voltage, reduce the fluctuation amplitude of the output voltage, and thus achieve the purpose of preventing the electrical equipment connected to the inverter from frequently tripping due to overvoltage protection.

[0070] See Figure 1 , a control method for an inverter may include:

[0071] Step S101: Obtain the input voltage of the three-phase rectifier circuit in the inverter.

[0072] The inverter includes a rectifier circuit, a filter circuit, an inverter circuit, and a control circuit. The rectifier circuit is used to convert the input AC power supply into a DC power supply. The filter circuit is used to eliminate the high-order harmonic components in the pulsating DC voltage output by the rectifier circuit to make the DC voltage smoother. The inverter circuit is used to convert the rectified and filtered DC power supply into an AC power supply with adjustable frequency and voltage for use by electrical equipment. The control circuit is used to output a modulation ratio to control the working state of the inverter circuit and is also used to monitor and protect the safe operation of the main circuit. Among them, the fluctuation amplitude of the output voltage of the inverter is directly controlled by the modulation ratio output by the control circuit.

[0073] When the input voltage of the three-phase rectifier circuit in the inverter fluctuates, it will drive the output voltage of the inverter to fluctuate. The fluctuation of the three-phase input voltage of the rectifier circuit of the inverter is the main cause of the frequent overvoltage protection shutdown of the electrical equipment connected to the inverter. Therefore, in this solution, it is necessary to preferentially detect the input voltage of the three-phase rectifier circuit.

[0074] When detecting the input voltage of the three-phase rectifier circuit, a voltage sensor can be used for measurement. Since the input voltage of the three-phase rectifier circuit is high voltage, in order to prevent damage to the detection circuit caused by high voltage, in this application, the voltage sensor can be an isolated voltage sensor.

[0075] Step S102: Determine whether the maximum value of the input voltage in the current cycle is within a first preset range.

[0076] This solution divides each time period into a cycle. In this step, the input voltage obtained within the current cycle is statistically analyzed to determine the maximum value Urs-max of each input voltage detected within the current cycle. The maximum value Urs-max of the input voltage is compared with the first preset range to determine whether the maximum value Urs-max of the input voltage is within the first preset range (VH1, VH2). When the maximum value Urs-max of the input voltage is within the first preset range (VH1, VH2), it indicates that the highest voltage within the current cycle is within the allowable range. Otherwise, it indicates that the maximum value of the input voltage in the current cycle is not within the allowable range. At this time, if the maximum value Urs-max of the input voltage is greater than VH2, then the maximum value of the input voltage in the current cycle is too high. If the maximum value Urs-max of the input voltage is less than VH1, then the maximum value of the input voltage in the current cycle is too low.

[0077] Step S103: Determine whether the minimum value of the input voltage within the current cycle is within the second preset range.

[0078] Statistically analyze the input voltage obtained within the current cycle to determine the minimum value Urs-min of each input voltage detected within the current cycle. The minimum value Urs-min of the input voltage is compared with the second preset range to determine whether the minimum value Urs-min of the input voltage is within the second preset range (VL1, VL2). When the minimum value Urs-min of the input voltage is within the second preset range (VL1, VL2), it indicates that the lowest voltage within the current cycle is within the allowable range. Otherwise, it indicates that the minimum value of the input voltage in the current cycle is not within the allowable range. At this time, if the minimum value Urs-min of the input voltage is greater than VL2, then the minimum value of the input voltage in the current cycle is too high. If the minimum value Urs-min of the input voltage is less than VL1, then the minimum value of the input voltage in the current cycle is too low.

[0079] Figure 2 It is a schematic diagram of the setting method of the first preset range (VH1, VH2) and the second preset range (VL1, VL2) disclosed in the embodiment of the present application.

[0080] Step S104: When the maximum value of the input voltage is not within the first preset range and / or the minimum value of the input voltage is not within the second preset range, calculate the compensation coefficient.

[0081] In this step, when it is detected that the maximum value of the input voltage is not within the first preset range or the minimum value of the input voltage is not within the second preset range, a corresponding compensation coefficient is calculated. In the present application, a mapping relationship between the maximum value of the input voltage and the compensation coefficient when the maximum value of the input voltage is not within the first preset range, a mapping relationship between the minimum value of the input voltage and the compensation coefficient when the minimum value of the input voltage is not within the second preset range, and a mapping relationship between the maximum value, the minimum value of the input voltage and the compensation coefficient when the maximum value is not within the first preset range and the minimum value is not within the second preset range can be established in advance. Based on this mapping relationship, the compensation coefficient can be quickly determined.

[0082] In this embodiment, when it is necessary to calculate the compensation coefficient, the corresponding compensation coefficient can be obtained by looking up a table based on the difference between the maximum value and the first reference value and the difference between the minimum value and the second reference value. That is, when the maximum value of the input voltage is not within the first preset range, calculate the difference between the maximum value of the input voltage and the first reference value, which is denoted as the first difference; when the minimum value of the input voltage is not within the second preset range, calculate the difference between the minimum value of the input voltage and the second reference value, which is denoted as the second difference.

[0083] The first reference value can be the average value of the first preset range, or when the maximum value is greater than the maximum value of the first preset range, the first reference value is the maximum value of the first preset range, and when the maximum value is less than the minimum value of the first preset range, the first reference value is the minimum value of the first preset range.

[0084] The second reference value can be the average value of the second preset range, or when the minimum value is greater than the maximum value of the second preset range, the second reference value is the maximum value of the second preset range, and when the minimum value is less than the minimum value of the second preset range, the second reference value is the minimum value of the second preset range.

[0085] After determining the first reference value and the second reference value, calculate the first difference between the maximum value of the input voltage and the first reference value and the second difference between the minimum value of the input voltage and the second reference value, and then look up the table based on the first difference and the second difference to obtain the compensation coefficient corresponding to the generated first difference and / or second difference. In this process, if only the first difference is generated, look up the table based on the first difference to obtain the corresponding compensation coefficient. If only the second difference is generated, look up the table based on the second difference to obtain the corresponding compensation coefficient. When both the first difference and the second difference are generated, look up the table based on both the first difference and the second difference to obtain the corresponding compensation coefficient.

[0086] Step S105: Adjust the output modulation ratio of the frequency converter based on the compensation coefficient.

[0087] In this step, after determining the compensation coefficient, the output modulation ratio of the frequency converter is adjusted based on the compensation coefficient to reduce the amplitude of the output voltage fluctuation of the frequency converter.

[0088] For the technical solution disclosed in the above embodiments of the present application, the input voltage of the three-phase rectifier circuit in the frequency converter is obtained, and it is judged whether the maximum value of the input voltage of the three-phase rectifier circuit collected in the current period is within the first preset range and whether the minimum value of the input voltage is within the second preset range. When the maximum value is not within the first preset range and / or the minimum value is not within the second preset range, a compensation coefficient is calculated, and the modulation ratio of the frequency converter is adjusted based on the compensation coefficient to reduce the amplitude of the output voltage fluctuation of the frequency converter, avoiding frequent over-voltage and under-voltage protection shutdowns of the electrical equipment powered by the frequency converter due to large fluctuations in the input voltage of the frequency converter.

[0089] Further, in addition to monitoring the amplitude of the fluctuation of the input voltage of the frequency converter, the bus voltage of the electrical equipment connected to the output end of the frequency converter can also be monitored, and the output modulation ratio of the frequency converter is adjusted based on the magnitude of the bus voltage to prevent the amplitude of the bus voltage fluctuation from being too large, thereby causing frequent over-voltage shutdowns of the electrical equipment. Specifically, referring to Figure 3 The above method may further include:

[0090] Step S301: Obtain the bus voltage of the electrical equipment connected to the output end of the frequency converter.

[0091] In this step, a voltage sensor or other voltage acquisition device is used to collect the bus voltage of the electrical equipment. The voltage sensor and voltage acquisition device can be an isolated voltage sensor and voltage acquisition device.

[0092] In this step, by real-time collecting the bus voltage Udc of the PN bus of the electrical equipment, the bus voltage Udc is output as a 0-3.3V voltage signal after differential proportional scaling, and this voltage signal is used as the sampled bus voltage and input to the DSP for subsequent logical judgment.

[0093] Step S302: Perform PI regulation based on the comparison result between the bus voltage and the reference voltage.

[0094] After the DSP obtains the bus voltage, it detects the change of the bus voltage in real time, compares the collected bus voltage with the given reference voltage Udc*, and sends the comparison result to the PI regulator to obtain the PI regulation result.

[0095] Step S303: Obtain a compensation coefficient that matches the output result of the PI regulation, and control the output modulation ratio of the frequency converter based on the compensation coefficient.

[0096] In this step, the collected bus voltage is compared with the given reference voltage Udc*, and the comparison result is sent to the PI regulator. Based on the preset mapping relationship, a compensation coefficient that matches the output result of the PI regulator is obtained, and the output modulation ratio of the frequency converter is controlled based on the compensation coefficient.

[0097] When the electrical equipment is a motor, the collected bus voltage is compared with the given reference voltage Udc*, and the comparison result is sent to the PI regulator to form a voltage outer loop. The output of the PI regulator serves as the reference for the current inner loop, and together with the voltage outer loop, closed-loop control is achieved. Its control block diagram is as Figure 4 shown, and the mathematical model is:

[0098]

[0099] Among them, the formula contains two parts of data. The first part is the output of the PI controller, which is used to eliminate the error of the d-axis current (i d -i d *). Here, s is the complex frequency variable in the Laplace transform, which is used to represent the dynamic characteristics of the system. The second part is the cross-coupling term. Due to the rotation (ω) of the motor, the q-axis current (i q ) will generate an induced voltage on the d-axis, and its magnitude is proportional to the inductance (L f ) and the rotational angular velocity (ω) of the motor.

[0100] The formula contains two parts of data. The first part is the output of the PI controller, which is used to eliminate the error of the q-axis current (i q -i q *). The second part is the negative value of the cross-coupling term, which represents the opposite of the induced voltage generated by the d-axis current (i d ) on the q-axis.

[0101] In motor control, the above formula is used to calculate the voltages u d and u q that need to be applied to the motor, and then further calculate the compensation coefficients corresponding to u d and u q . Based on the compensation coefficients, the output modulation ratio of the frequency converter is controlled so as to control the current at the desired d-axis and q-axis values (i d * and i q *).

[0102] The technical solution disclosed in the above embodiments detects the change of the bus voltage in real time. When the bus voltage changes, a compensation technique is also adopted in real time. The PI regulator uses the PI technique to calculate the PI adjustment result according to the magnitude and direction of the deviation, and then determines the compensation coefficient that matches the output result of the PI regulator. The modulation ratio of the pulse modulation output by the frequency converter is adjusted through this compensation coefficient, so as to respond to the voltage change of the power grid in real time, reduce the fluctuation amplitude of the bus voltage, and avoid frequent over-voltage and under-voltage protection shutdown of the frequency converter and the unit due to large input voltage fluctuations.

[0103] Further, corresponding to the above method, the present application also discloses a control circuit of a frequency converter. Refer to Figure 5 and this circuit may include:

[0104] An input voltage detection circuit 10 for obtaining the input voltage of the three-phase rectifier circuit in the frequency converter;

[0105] A voltage change analysis circuit 20 for determining whether the maximum value of the input voltage in the current cycle is within a first preset range; and determining whether the minimum value of the input voltage in the current cycle is within a second preset range;

[0106] A compensation coefficient calculation circuit 30 for calculating a compensation coefficient when the maximum value of the input voltage is not within the first preset range or the minimum value of the input voltage is not within the second preset range;

[0107] A modulation circuit 40 for adjusting its own output modulation ratio based on the compensation coefficient.

[0108] In addition, the present application also discloses a structural schematic diagram of an input voltage detection circuit. Refer to Figure 5 and the input voltage detection circuit includes:

[0109] A first comparator U1 and the peripheral circuit of the first comparator U1;

[0110] The non-inverting input terminal of the first comparator U1 is used to obtain the voltage Us of the S phase line in the input voltage of the three-phase rectifier circuit and the reference voltage Vref;

[0111] The inverting input terminal of the first comparator U1 is used to obtain the voltage Ur of the R phase line in the input voltage of the three-phase rectifier circuit.

[0112] Refer to Figure 6 and the peripheral circuit in the input voltage detection circuit includes:

[0113] A first resistor R1, the first end of the first resistor R1 is connected to the R phase line in the input voltage of the three-phase rectifier circuit, and the second end of the first resistor R1 is connected to the inverting input terminal of the first comparator;

[0114] A second resistor R2, with the first end of the second resistor R2 connected to the S-phase line of the input voltage of the three-phase rectifier circuit, and the second end of the first resistor R1 connected to the non-inverting input terminal of the first comparator;

[0115] A third resistor R3, with the first end of the third resistor R3 obtaining the reference voltage, and the second end of the third resistor R3 connected to the non-inverting input terminal of the first comparator;

[0116] A fourth resistor R4, with the first end of the fourth resistor R4 connected to the inverting input terminal of the first comparator, and the second end of the fourth resistor R4 connected to the output terminal of the first comparator;

[0117] A fifth resistor R5, with the first end of the fifth resistor R5 connected to the output terminal of the first comparator, and the second end of the fifth resistor R5 serving as the output terminal of the input voltage detection circuit;

[0118] A first capacitor C1, with the first end of the first capacitor C1 connected to the inverting input terminal of the first comparator, and the second end of the first capacitor C1 grounded;

[0119] A second capacitor C2, with the first end of the second capacitor C2 connected to the non-inverting input terminal of the first comparator, and the second end of the second capacitor C2 grounded;

[0120] A third capacitor C3, with the third capacitor C3 connected in parallel with the third resistor R3;

[0121] A fourth capacitor C4, with the fourth capacitor C4 connected in parallel with the fourth resistor R4;

[0122] A fifth capacitor C5, with the first end of the fifth capacitor C5 connected to the second end of the fifth resistor R5, and the second end of the fifth capacitor C5 grounded.

[0123] Figure 6 The shown input voltage detection circuit collects the input voltages Ur and Us of the three-phase rectifier circuit in real time, and uses the first comparator to perform differential proportional scaling on Ur and Us and add a Vref bias, so that the difference between the two collected voltages is between 0 - 3.3V (which can be calibrated according to user requirements), and sends the output result of the first comparator to the DSP (compensation coefficient calculation circuit) for subsequent analysis and judgment.

[0124] Corresponding to the above method, see Figure 5 and this circuit may further include

[0125] A bus voltage detection circuit 50 for obtaining the bus voltage of the electrical equipment connected to the output terminal of the frequency converter;

[0126] The compensation coefficient calculation circuit 30 is further configured to perform PI regulation based on the comparison result between the bus voltage and the reference voltage; obtain a compensation coefficient matching the output result of the PI regulation, and control the output modulation ratio of the frequency converter based on the compensation coefficient.

[0127] See Figure 7 , the bus voltage detection circuit includes:

[0128] A second comparator U2, a third comparator U3, and peripheral circuits;

[0129] The inverting input terminal of the second comparator U2 is connected to the N-phase line in the bus of the electrical device, and the non-inverting input terminal of the second comparator U2 is connected to the P-phase line in the bus of the electrical device;

[0130] The inverting input terminal of the third comparator U3 is connected to the output terminal of the third comparator U3, and the non-inverting input terminal of the third comparator U3 is connected to the output terminal of the second comparator U2.

[0131] See Figure 7 , the peripheral circuits in the bus voltage detection circuit include:

[0132] A sixth resistor R6, the first end of the sixth resistor R6 is connected to the N-phase line in the bus of the electrical device, and the second end of the sixth resistor R6 is connected to the inverting input terminal of the second comparator U2;

[0133] A seventh resistor R7, the first end of the seventh resistor R7 is connected to the P-phase line in the bus of the electrical device, and the second end of the seventh resistor R7 is connected to the non-inverting input terminal of the second comparator U2;

[0134] An eighth resistor R8, the first end of the eighth resistor R8 is connected to the non-inverting input terminal of the second comparator U2, and the second end of the eighth resistor R8 is grounded;

[0135] A ninth resistor R9, the first end of the ninth resistor R9 is connected to the inverting input terminal of the second comparator U2, and the second end of the ninth resistor R9 is connected to the output terminal of the second comparator U2;

[0136] A tenth resistor R10, the first end of the tenth resistor R10 is connected to the output terminal of the third comparator U3, and the second end of the tenth resistor R10 serves as the output terminal of the bus voltage detection circuit;

[0137] A sixth capacitor C6, the sixth capacitor C6 is connected in parallel with the eighth resistor R8;

[0138] The seventh capacitor C7, and the seventh capacitor C7 is connected in parallel with the ninth resistor R9.

[0139] See Figure 7 , the bus voltage Udc collected by the bus voltage detection circuit is output as a voltage signal of 0 - 3.3V (or other calibrated amplitude) to the DSP for subsequent analysis and judgment after differential proportional scaling.

[0140] In order to verify the technical effects of the above circuit, the present application also measures the output of the frequency converter in scenarios where the grid voltage is 310VAC and 515VAC. See Figure 8 and Figure 9 , Figure 8 is the output voltage waveform diagram of the frequency converter when the grid voltage is 310VAC, Figure 9 is the output voltage waveform diagram of the frequency converter when the grid voltage is 515VAC. From Figure 8 and Figure 9 , it can be seen that whether in the grid voltage scenario of 310VAC or 515VAC, the frequency converter can output a voltage signal with a stable amplitude, thereby ensuring that the electrical equipment will not be frequently started and stopped due to grid fluctuations.

[0141] Corresponding to the circuit, the present application also discloses a frequency converter, including the control circuit of the frequency converter described in any one of the above.

[0142] Corresponding to the above frequency converter, the present application also discloses an electrical equipment, and this electrical equipment includes the above frequency converter.

[0143] For the convenience of description, when describing the above system, it is divided into various modules according to functions for separate description. Of course, when implementing the present invention, the functions of each module can be implemented in the same or multiple software and / or hardware.

[0144] Each embodiment in this specification is described in a progressive manner. For the same or similar parts between each embodiment, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple. For the relevant parts, reference can be made to the partial description of the method embodiment. The system and system embodiments described above are only illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place, or may be distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative work.

[0145] Those skilled in the art may further realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of the two. To clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods for each specific application to implement the described functions, but such implementation should not be considered to exceed the scope of the present invention.

[0146] The steps of the methods or algorithms described in combination with the embodiments disclosed herein can be directly implemented by hardware, software modules executed by a processor, or a combination of the two. The software modules can be placed in a random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium well-known in the technical field.

[0147] It should also be noted that in this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0148] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for a frequency converter, characterized in that, Including: Obtain the input voltage of the three-phase rectifier circuit in the frequency converter; Judge whether the maximum value of the input voltage in the current cycle is within a first preset range; Judge whether the minimum value of the input voltage in the current cycle is within a second preset range; When the maximum value of the input voltage is not within the first preset range and / or the minimum value of the input voltage is not within the second preset range, calculate a compensation coefficient; Adjust the output modulation ratio of the frequency converter based on the compensation coefficient.

2. The control method of the frequency converter according to claim 1, characterized in that Also including: Obtain the bus voltage of the electrical equipment connected to the output end of the frequency converter; Perform PI regulation based on the comparison result of the bus voltage and the reference voltage; Obtain a compensation coefficient matching the output result of the PI regulation, and control the output modulation ratio of the frequency converter based on the compensation coefficient.

3. The control method of the frequency converter according to claim 1, characterized in that When the maximum value of the input voltage is not within the first preset range or the minimum value of the input voltage is not within the second preset range, calculating a compensation coefficient includes: When the maximum value of the input voltage is not within the first preset range, calculate the difference between the maximum value of the input voltage and a first reference value, denoted as the first difference; When the minimum value of the input voltage is not within the second preset range, calculate the difference between the minimum value of the input voltage and a second reference value, denoted as the second difference; When it is detected that the first difference and / or the second difference is generated, obtain a compensation coefficient matching the generated difference based on a preset mapping table.

4. A control circuit of an inverter, characterized in that, Including: An input voltage detection circuit for obtaining the input voltage of the three-phase rectifier circuit in the frequency converter; A voltage change analysis circuit for judging whether the maximum value of the input voltage in the current cycle is within a first preset range; judging whether the minimum value of the input voltage in the current cycle is within a second preset range; A compensation coefficient calculation circuit for calculating a compensation coefficient when the maximum value of the input voltage is not within the first preset range or the minimum value of the input voltage is not within the second preset range; A modulation circuit for adjusting its own output modulation ratio based on the compensation coefficient.

5. The control circuit of the frequency converter according to claim 4, characterized in that, The input voltage detection circuit includes: A first comparator and the peripheral circuit of the first comparator; The non-inverting input terminal of the first comparator is used to obtain the voltage of the S phase line and the reference voltage in the input voltage of the three-phase rectifier circuit; The inverting input terminal of the first comparator is used to obtain the voltage of the R phase line in the input voltage of the three-phase rectifier circuit.

6. The control circuit of the frequency converter according to claim 5, characterized in that, The peripheral circuit in the input voltage detection circuit includes: A first resistor, the first end of the first resistor is connected to the R phase line in the input voltage of the three-phase rectifier circuit, and the second end of the first resistor is connected to the inverting input terminal of the first comparator; A second resistor, the first end of the second resistor is connected to the S phase line in the input voltage of the three-phase rectifier circuit, and the second end of the first resistor is connected to the non-inverting input terminal of the first comparator; A third resistor, the first end of the third resistor obtains the reference voltage, and the second end of the third resistor is connected to the non-inverting input terminal of the first comparator; A fourth resistor, a first end of the fourth resistor is connected to an inverting input terminal of the first comparator, and a second end of the fourth resistor is connected to an output terminal of the first comparator; A fifth resistor, a first end of the fifth resistor is connected to the output terminal of the first comparator, and a second end of the fifth resistor serves as an output terminal of the input voltage detection circuit; A first capacitor, a first end of the first capacitor is connected to the inverting input terminal of the first comparator, and a second end of the first capacitor is grounded; A second capacitor, a first end of the second capacitor is connected to a non-inverting input terminal of the first comparator, and a second end of the second capacitor is grounded; A third capacitor, the third capacitor is connected in parallel with the third resistor; A fourth capacitor, the fourth capacitor is connected in parallel with the fourth resistor; A fifth capacitor, a first end of the fifth capacitor is connected to the second end of the fifth resistor, and a second end of the fifth capacitor is grounded.

7. The control circuit of the frequency converter according to claim 5, characterized in that, Further comprising: A bus voltage detection circuit for obtaining a bus voltage of an electrical device connected to an output terminal of the frequency converter; The compensation coefficient calculation circuit is further configured to perform PI regulation based on a comparison result between the bus voltage and a reference voltage; obtain a compensation coefficient matching an output result of the PI regulation, and control an output modulation ratio of the frequency converter based on the compensation coefficient.

8. The control circuit of the frequency converter according to claim 7, characterized in that, The bus voltage detection circuit includes: A second comparator, a third comparator and a peripheral circuit; An inverting input terminal of the second comparator is connected to an N-phase line in the bus of the electrical device, and a non-inverting input terminal of the second comparator is connected to a P-phase line in the bus of the electrical device; An inverting input terminal of the third comparator is connected to an output terminal of the third comparator, and a non-inverting input terminal of the third comparator is connected to an output terminal of the second comparator.

9. The control circuit of the frequency converter according to claim 8, characterized in that The peripheral circuit in the bus voltage detection circuit includes: A sixth resistor, a first end of the sixth resistor is connected to the N-phase line in the bus of the electrical device, and a second end of the sixth resistor is connected to the inverting input terminal of the second comparator; A seventh resistor, a first end of the seventh resistor is connected to the P-phase line in the bus of the electrical device, and a second end of the seventh resistor is connected to the non-inverting input terminal of the second comparator; An eighth resistor, a first end of the eighth resistor is connected to the non-inverting input terminal of the second comparator, and a second end of the eighth resistor is grounded; A ninth resistor, a first end of the ninth resistor is connected to the inverting input terminal of the second comparator, and a second end of the ninth resistor is connected to the output terminal of the second comparator; A tenth resistor, a first end of the tenth resistor is connected to the output terminal of the third comparator, and a second end of the tenth resistor serves as an output terminal of the bus voltage detection circuit; A sixth capacitor, the sixth capacitor is connected in parallel with the eighth resistor; A seventh capacitor, the seventh capacitor is connected in parallel with the ninth resistor.

10. A frequency converter, characterized in that, Comprising the control circuit of the frequency converter according to any one of claims 4-9.

11. An electrical device, characterized in that, Comprising the frequency converter according to claim 10.

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