A method for series voltage equalization control of power devices in a frequency converter

Abstract

This invention discloses a series voltage equalization control method for power devices in a frequency converter. First, the total bus voltage across each series power device in the frequency converter is obtained, and based on the desired voltage values ​​across the devices, a series device equalization coefficient is calculated. Proportional-integral (PI) adjustment is performed on the voltage across the devices. Based on the output voltage result, the series device equalization coefficient corrects the modulation wave of each device. The obtained modulation wave is compared with the carrier wave to generate a PWM signal, controlling the devices to dynamically equalize voltage. This patented method solves the problem of uneven voltage distribution among series power devices and achieves dynamic equalization during the operation of each power device.

Description

Technical Field

[0001] This invention belongs to the field of power electronic equipment control, and particularly relates to a series voltage equalization control method for power devices in a frequency converter. Background Technology

[0002] In the field of marine propulsion frequency converter systems, series operation of devices is a simple and effective solution for increasing voltage and expanding capacity to meet the application requirements of medium-voltage, high-power, and high-efficiency applications. Series operation of power devices in frequency converters has advantages such as high efficiency, high reliability, and low cost, while voltage stress balancing between devices is the core challenge of series operation.

[0003] The continuous increase in DC voltage levels has led to a growing demand for series applications of power devices. Currently, the common method to solve the voltage equalization problem in power devices is to add snubber circuits. Snubber circuits are mostly composed of capacitors, resistors, inductors, and diodes. These snubber circuits occupy a large volume, are costly, and are complex to install.

[0004] In recent years, the power density of frequency converters has been increasing. Adding a snubber circuit will significantly reduce the power density of the frequency converter. At the same time, the components in the snubber circuit will introduce additional power losses, reducing the efficiency of the frequency converter. The dynamic characteristics of the snubber circuit are determined by the electrical parameters of the components themselves and lack dynamic adjustment capability. Summary of the Invention

[0005] The purpose of this invention is to address the root cause of the above-mentioned problems by proposing a series voltage equalization control method for inverter power devices with excellent dynamic and static response performance.

[0006] The technical solution adopted by this invention to solve its technical problem is: a series voltage equalization control method for power devices in a frequency converter, comprising the following steps:

[0007] (1) Obtain the total bus voltage value after all power devices of the inverter are connected in series, and the voltage value across each power device;

[0008] (2) Detect the voltage value across each power device, calculate the imbalance coefficient based on the detected voltage value, calculate the desired voltage value across the device based on the total bus voltage value and the number of series power devices, and limit the imbalance coefficient to be less than the trigger value of 1.1;

[0009] (3) When the calculated imbalance coefficient is greater than 1.1, the voltage value across each power device is calculated by proportional-integral regulation, the output result of proportional-integral regulation is limited, and the output result is used as the modulation wave of the power device drive signal.

[0010] (4) The generated modulation wave is compared with the carrier wave to generate a PWM signal, which controls the power device to dynamically equalize the voltage.

[0011] The series voltage equalization control method for power devices in a frequency converter, wherein the desired voltage value U across the device in step (2) is... d =U / n, where U is the total bus voltage borne by the series devices and n is the number of series power devices.

[0012] The series voltage equalization control method for power devices in a frequency converter, wherein the imbalance coefficient in step (2) Among them U d (n) represents the detected voltage value across the nth power device, U d (n)max is the maximum voltage value detected, and fn is the obtained imbalance coefficient.

[0013] In the series voltage equalization control method for power devices in a frequency converter, step (3) involves inputting the desired voltage value across the device, comparing the actual measured voltage value across the device with the desired voltage value, performing proportional-integral adjustment calculation on the difference, and outputting the calculation result. Where K p K is the proportional coefficient. i Here, is the coefficient of the integral element, and e(t) is the difference between the desired voltage across the device and the actual measured voltage across the device.

[0014] The series voltage equalization control method for power devices of a frequency converter, in step (3), limits the calculation results by setting the minimum value of the output result to zero and the maximum value of the output result to the upper limit value, where the upper limit value is the maximum operating current of the frequency converter.

[0015] The aforementioned inverter power device series voltage equalization control method uses IGCT, IEGT, or MOSFET as the power device.

[0016] The beneficial effects of this invention are: when the imbalance coefficient is greater than 1.1, the method of this invention performs proportional-integral adjustment calculation on the voltage value across each power device, limits the output result of the proportional-integral adjustment, and uses the output result as the modulation wave of the power device drive signal, making the correction of the control method more convenient, effectively solving the problems of complex and costly power semiconductor absorption circuits and poor equalization performance, and realizing the dynamic balance of the series voltage of multiple devices. Attached Figure Description

[0017] Figure 1 This is a flowchart of the control method according to an embodiment of the present invention;

[0018] Figure 2 This is a circuit diagram showing the series connection of power devices in a frequency converter according to an embodiment of the present invention;

[0019] Figure 3This describes the circuit connection relationship of the series power devices in the multilevel inverter of the present invention. Detailed Implementation

[0020] To further illustrate the objectives and technical solutions of this invention, the invention will be described in more detail below with reference to specific embodiments in conjunction with the accompanying drawings. The following embodiments are for illustrative purposes only and do not constitute a limitation thereof.

[0021] Reference Figure 1 As shown, this invention discloses a series voltage equalization control method for power devices in a frequency converter, which effectively solves the problems of complex and costly power semiconductor absorption circuits and poor equalization performance, and achieves dynamic balance of the series voltage of multiple devices; specifically, it includes the following steps:

[0022] (1) Obtain the total bus voltage value after each power device of the inverter is connected in series, and the voltage value across each power device. The power devices include power electronic devices such as IGCT, IEGT, and MOSFET that are controlled to be switched on and off by drive signals.

[0023] (2) Detect the voltage value across each power device, calculate the imbalance coefficient based on the detected voltage, calculate the desired voltage value across the device based on the total bus voltage and the number of series power devices, and limit the imbalance coefficient to be less than the trigger value of 1.1.

[0024] In this implementation example, the desired voltage value across the device is calculated by dividing the total bus voltage U across the series-connected devices by the number of series-connected devices n, thus obtaining the desired voltage U for each series-connected device. d The calculation formula is as follows:

[0025] U d =U / n.

[0026] The imbalance coefficient is obtained by the following formula:

[0027]

[0028] Among them, U d (n) represents the detected voltage value across the nth power device, U d (n)max is the maximum voltage value detected, and fn is the obtained imbalance coefficient.

[0029] Ud(n) is the detected value of the voltage across the nth device, U d (n)max is the maximum detected voltage value, f n The obtained imbalance coefficient is denoted as .

[0030] (3) When the calculated imbalance coefficient is greater than 1.1, the voltage value across each power device is calculated by proportional-integral adjustment, the output result of proportional-integral adjustment is limited, and the output result is used as the modulation wave of the power device drive signal.

[0031] The series voltage proportional-integral (PI) adjustment calculation involves inputting the desired voltage value across the device, comparing the actual measured voltage value across the device with the desired value, and then performing a PI adjustment calculation on the difference. The calculation formula is as follows:

[0032]

[0033] Where K p K is the proportional coefficient. i Let K be the coefficient of the integral element, e(t) be the difference between the desired voltage across the device and the actual measured voltage across the device, and u(t) be the calculated output. In a proportional-integral (PI) serial control structure, the proportional element affects the system gain, and the integral element affects the system bandwidth. The two are independent, or in other words, Ki = Ki. p and K i The adjustment can decouple the series voltage control.

[0034] Limiting the calculation results involves setting the minimum output value to zero and setting the maximum output value to the upper limit value, which is the maximum operating current of the frequency converter.

[0035] (4) The generated modulation wave is compared with the carrier wave to generate a PWM signal, which controls the power device to dynamically equalize the voltage.

[0036] Figure 2 The series circuit connection relationship of power devices in the multilevel inverter provided in this invention includes a drive signal, power devices and a voltage detection module. Figure 3 The circuit connection relationship of the power device series circuit in a multilevel inverter is provided as another embodiment of the present invention.

[0037] The aforementioned series circuit of power devices refers to a structure in which the emitters T1 and collectors T2 of the power electronic devices are connected, and the positive terminal of the reverse diode D1 is connected to the negative terminal of D2. The voltage detection module is used to acquire the voltage values ​​of each series device; the series device drive signal modulation wave calculation module corrects and limits the output result of the proportional-integral regulation of the series device voltage based on the voltage balance coefficient of each series device to obtain the modulated wave of the drive signal for each device; the PWM pulse generation module compares the modulated wave of the series device drive signal with the carrier wave to generate a PWM signal.

[0038] The above embodiments are merely illustrative of the principles and effects of the present invention, as well as some of the application examples. For those skilled in the art, various modifications and improvements can be made without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for series voltage equalization control of power devices in a frequency converter, characterized in that: Includes the following steps: (1) Obtain the total bus voltage value after each power device of the inverter is connected in series, and the voltage value across each power device, wherein the power device is an IGCT, IEGT or MOSFET; (2) Detect the voltage across each power device, calculate the imbalance coefficient, and calculate the desired voltage across the device based on the total bus voltage and the number of series-connected power devices. U d = U / n The imbalance coefficient is limited to be less than the trigger value of 1.1, where U The total bus voltage borne by the series-connected devices. n The number of series power devices, and the imbalance factor. ,in U d (n) This is the detected value of the voltage across the nth power device; (3) When the calculated imbalance coefficient is greater than 1.1, the proportional-integral adjustment calculation is performed on the voltage value across each power device. The minimum value of the output result is set to zero, and the maximum value of the output result is set to the upper limit value, which is the maximum operating current of the frequency converter. The output result is used as the modulation wave of the power device drive signal. The series voltage proportional-integral adjustment calculation is to input the desired voltage value across the device, compare the actual measured voltage value across the device with the desired voltage value across the device, perform proportional-integral adjustment calculation on the difference, and output the calculation result. ,in K p This is the coefficient for the proportional element. K i The coefficients of the integral element, e ( t The difference between the expected voltage across the device and the actual measured voltage across the device is denoted as . (4) The generated modulation wave is compared with the carrier wave to generate a PWM signal, which controls the power device to dynamically equalize the voltage.

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