A single-vector temperature control frequency conversion control method based on a three-phase PWM rectifier

Abstract

The present invention provides a single-vector temperature control variable-frequency control method based on a three-phase PWM rectifier, which relates to the technical field of power electronic power conversion; first, for the three-phase PWM rectifier, an objective function for IGBT and power quality is established by using the relationship between the AC-side voltages of the three-phase PWM rectifier to select the switching state; by collecting the temperature of the IGBT, a mathematical relationship is constructed to change the switching frequency of the IGBT, thereby reducing the heat generation of the IGBT to avoid damage to the IGBT; the present invention establishes an objective function for IGBT and power quality to comprehensively select the switching state, and also takes into account the stability of the DC-side voltage and the temperature characteristics of the IGBT to perform variable-frequency modulation on the driving frequency.

Description

Technical Field

[0001] This invention relates to the field of power electronics and power conversion technology, and in particular to a single-vector temperature control frequency converter based on a three-phase PWM rectifier. Background Technology

[0002] With the development of power electronics technology, the research on microgrid hubs has also developed rapidly. The rectifier side, as the head equipment of the microgrid hub, often needs to bear a large power transmission. The demand for high-power rectifier equipment is increasing. Since three-phase PWM rectifiers have the characteristic of controlling the bidirectional flow of energy, they are widely used in high-power rectifier equipment.

[0003] Current three-phase PWM rectifiers are important high-power devices with large currents flowing through the switching transistors. Since the losses of the switching transistors are composed of both turn-on and conduction losses, the temperature control of the IGBTs becomes very important. When the temperature exceeds the IGBT's limit, it often causes irreversible damage, resulting in the device failing to work properly. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention presents a single-vector temperature-controlled frequency converter method based on a three-phase PWM rectifier.

[0005] A single-vector temperature control frequency converter based on a three-phase PWM rectifier includes the following steps:

[0006] Step 1: For a three-phase PWM rectifier, the switching state is selected by establishing an objective function for IGBT and power quality using the relationship between the AC voltage measurements of the three-phase PWM rectifier.

[0007] Step 1.1: Use the AC voltage sampling circuit in the control circuit to acquire the A, B, and C phase voltages of the three-phase PWM rectifier, and use the DC voltage sampling circuit in the control circuit to acquire the DC side voltage v of the rectifier. dc The Hall current sampling circuit in the control circuit is used to collect the current of the three phases A, B, and C.

[0008] Step 1.2: Establish the time-domain model of the rectifier based on Kirchhoff's voltage law, and obtain the following relationship after two-phase rotation transformation:

[0009]

[0010] Where i α i β e α e β The grid-side current and voltage in the three-phase stationary coordinate system are converted to the grid-side current and voltage in the two-phase stationary coordinate system, respectively. α vβ To convert AC voltage measurement to AC voltage measurement in a two-phase stationary coordinate system, R is the grid-side equivalent resistance and L is the grid-side inductance;

[0011] Step 1.3: After transforming the formula described in Step 1.2 using the forward Euler method, obtain the current value i in the two-phase stationary coordinate system at time k+1. α (k+1), i β (k+1) specifically refers to:

[0012]

[0013] Where v α (k), v β (k), i α (k), i β (k), e α (k), e β (k) is i α i β e α e β v α v β The value of i at time k. α (k+1), i β (k+1) is i α i β The value at time k+1;

[0014] Step 1.4: Establish calculation i α (k+1) and reference value The objective function 1 for the error is optimal, where the deviation between the predicted and actual values ​​is minimized when the objective function value is minimized. The objective function 1 is set as follows:

[0015]

[0016] Where λ1 and λ2 are artificially given active current weighting coefficients and reactive current weighting coefficients, respectively. The predicted current value for the α-axis is given by: The predicted current value for the β-axis is obtained using a DC-side reference value. With the DC side voltage v of the three-phase PWM rectifier dc The difference is processed through a PI circuit to obtain the predicted α-axis current value in the two-phase stationary coordinate system after two-phase rotation to two-phase stationary coordinate transformation. β-axis predicted current value

[0017] Step 1.5: Traverse all switching states of the three-phase PWM rectifier. The three-phase PWM rectifier has eight switching states, therefore each predicted switching state corresponds to a different v. αv β Therefore, this corresponds to the eight predicted types of i. α (k+1), i β (k+1), thus obtaining the values ​​of eight objective functions F;

[0018] Step 1.6: Collect the current temperature of the IGBTs. If the warning temperature is set to T0 and the limit temperature to TMAX, and the three-phase PWM rectifier has a total of 6 IGBTs, if the temperature of all 6 IGBTs is lower than the warning temperature T0, then the switching sequence corresponding to the minimum value of the objective function F set in Step 1.4 is selected as the current switching state output. If the temperature of any of the 6 IGBTs exceeds T0, then objective function 2 is established as follows:

[0019] F 1 =F + T1 + T2 + T3

[0020] Where T1 represents the temperature coefficient of the first bridge arm. If the temperatures of both IGBTs in the first bridge arm are less than T0 after being collected by the temperature sensor, or if the predicted switching state does not change, then T1 = 0. If the temperatures of both IGBTs in the first bridge arm are greater than or equal to T0 after being collected by the temperature sensor, and the predicted switching state changes, then the expression for T1 is as follows:

[0021]

[0022] Where T2 represents the temperature coefficient of the first bridge arm. If the temperatures of the two IGBTs in the second bridge arm are both less than T0 after being collected by the temperature sensor, or if the predicted switching state does not change, then T1 = 0. If the temperatures of the two IGBTs in the first bridge arm are both greater than or equal to T0 after being collected by the temperature sensor, and the predicted switching state changes, then the expression for T2 is as follows:

[0023]

[0024] Where T3 represents the temperature coefficient of the first bridge arm. If the temperatures of both IGBTs in the first bridge arm are less than T0 after being collected by the temperature sensor, or if the predicted switching state does not change, then T3 = 0. If the temperatures of both IGBTs in the first bridge arm are greater than or equal to T0 after being collected by the temperature sensor, and the predicted switching state changes, then the expression for T3 is as follows:

[0025]

[0026] Step 1.7: Traverse the objective function 2 of the eight switch states, select the smallest objective function 2 value as the current output switch state, and emit the driving waveform.

[0027] Step 2: By collecting the temperature of the IGBT, a mathematical relationship is constructed to change the switching frequency of the IGBT, thereby reducing the heat generation of the IGBT to avoid damage to the IGBT;

[0028] Step 2.1: Collect the temperature values of the 6 IGBTs on the three-phase PWM rectifier through a temperature sensor;

[0029] Step 2.2: Establish a frequency reduction function with the IGBT case temperature T as the independent variable as follows:

[0030]

[0031] Step 2.2: Establish a compensation frequency function with the DC voltage value v dc of the rectifier as the independent variable:

[0032]

[0033] Vdc* is the DC side voltage set value of the three-phase PWM rectifier;

[0034] Step 2.3: Carry out control design on the driving waveform frequency output by the rectifier to the IGBT through the DSP control chip. The control steps are as follows:

[0035] Set the initial value of the frequency reduction parameter to 1. At the kth moment, collect the current six-way IGBT temperature value T. If the current temperature T < the output value of the frequency reduction function is 1, then set the frequency reduction parameter jp unchanged. If the value of the frequency reduction parameter jp is 1, the DSP does not perform additional processing, and it is default that the three-phase PWM rectifier works in the normal state;

[0036] If the current six-way TGBT temperature value T > T0, set the jp value at the (K + 1)th moment to 2. When the system initially works, the carrier frequency and the driving waveform frequency are the same, both being f. At this time, change the current driving waveform frequency f to the following frequency f0. During the time, set the jp value to 2, and after the time, set the frequency reduction parameter value to 3:

[0037]

[0038] When the jp value of the system is 2, the DSP does not perform additional processing. When the jp value of the system is 3, the DSP collects the temperature of the IGBT. When the temperature T < T0, set the jp value to 1 and set the driving waveform frequency to f.

[0039] The beneficial effects produced by the present invention are as follows:

[0040] This technical solution provides a single-vector temperature-controlled frequency conversion control strategy based on a three-phase PWM rectifier, relating to the field of power electronics energy conversion technology. Currently, three-phase PWM rectification technology is a crucial device for AC-DC conversion, frequently used in high-power applications. As power increases, the current in the circuit correspondingly increases. The losses of the switching transistors consist of both turn-on and conduction losses. Conduction losses are unavoidable under high power conditions, while switching losses are frequency-dependent. If these losses are not controlled, they accumulate as heat. When the temperature exceeds the switching transistor's limit, irreversible damage often occurs. Therefore, it is necessary to dynamically control the operating frequency of the three-phase PWM rectifier's switching transistors, considering DC-side power quality, to achieve continuous operation of the three-phase PWM system under high power. This strategy first establishes an objective function for IGBTs and power quality to comprehensively select the appropriate switching state. It also considers the stability of the DC-side voltage and the temperature characteristics of the IGBTs to modulate the drive frequency. Attached Figure Description

[0041] Figure 1 This is a flowchart illustrating the overall process of the method of the present invention.

[0042] Figure 2 This is a schematic diagram of the frequency reduction control principle of the three-phase PWM rectifier of the present invention. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and embodiments;

[0044] A single-vector temperature control frequency converter based on a three-phase PWM rectifier is shown in the attached figure. Figure 1 As shown; including the following steps:

[0045] Step 1: For the three-phase PWM rectifier, the switching state is selected by establishing an objective function for the IGBT and power quality based on the relationship between the AC voltage measurements of the three-phase PWM rectifier; the frequency reduction control principle diagram of the three-phase PWM rectifier is attached. Figure 2 As shown;

[0046] Step 1.1: The controller acquires the information input from the three-phase PWM rectifier circuit. This requires acquiring the three-phase input voltage and current information, as well as the DC-side voltage. Then, using a predictive model, it predicts the sector where the three-phase PWM rectifier is located within the current control cycle. Combining temperature and frequency conversion control, it selects the drive waveform output by the three-phase PWM rectifier. Specifically, it uses a voltage sampling circuit in the control circuit to acquire the voltage v of the three phases A, B, and C of the three-phase PWM rectifier and the DC-side voltage. dc The Hall current sampling circuit collects the current of the three phases A, B, and C.

[0047] Step 1.2: Establish the time-domain model of the rectifier based on Kirchhoff's voltage law, and obtain the following relationship after two-phase rotation transformation:

[0048]

[0049] Where i α i β e α e β The grid-side current and voltage in the three-phase stationary coordinate system are converted to the grid-side current and voltage in the two-phase stationary coordinate system, respectively. α v β To convert AC voltage measurement to AC voltage measurement in a two-phase stationary coordinate system, R is the grid-side equivalent resistance and L is the grid-side inductance;

[0050] Step 1.3: After transforming the formula described in Step 1.2 using the forward Euler method, obtain the current value i in the two-phase stationary coordinate system at time k+1. α (k+1), i β (k+1) specifically refers to:

[0051]

[0052] Where v α (k), v β (k), i α (k), i β (k), e α (k), e β (k) is i α i β e α e β v α v β The value of i at time k. α (k+1), i β (k+1) is i α i β The value at time k+1;

[0053] Step 1.4: Establish calculation i α (k+1) and reference value The objective function 1 for the error is optimal, where the deviation between the predicted and actual values ​​is minimized when the objective function value is minimized. The objective function 1 is set as follows:

[0054]

[0055] Where λ1 and λ2 are artificially given active current weighting coefficients and reactive current weighting coefficients, respectively. The predicted current value for the α-axis is given by: The predicted current value for the β-axis is obtained using a DC-side reference value. With the DC side voltage v of the three-phase PWM rectifier dc The difference is processed through a PI circuit to obtain the predicted α-axis current value in the two-phase stationary coordinate system after two-phase rotation to two-phase stationary coordinate transformation. β-axis predicted current value

[0056] Step 1.5: Traverse all switching states of the three-phase PWM rectifier. The three-phase PWM rectifier has eight switching states, therefore each predicted switching state corresponds to a different v. α v β Therefore, this corresponds to the eight predicted types of i. α (k+1), i β (k+1), thus obtaining the values ​​of eight objective functions F;

[0057] Step 1.6: Collect the current temperature of the IGBTs. If the warning temperature is set to T0 and the limit temperature to TMAX, and the three-phase PWM rectifier has a total of 6 IGBTs, if the temperature of all 6 IGBTs is lower than the warning temperature T0, then the switching sequence corresponding to the minimum value of the objective function F set in Step 1.4 is selected as the current switching state output. If the temperature of any of the 6 IGBTs exceeds T0, then objective function 2 is established as follows:

[0058] F 1 =F + T1 + T2 + T3

[0059] Where T1 represents the temperature coefficient of the first bridge arm. If the temperatures of both IGBTs in the first bridge arm are less than T0 after being collected by the temperature sensor, or if the predicted switching state does not change, then T1 = 0. If the temperatures of both IGBTs in the first bridge arm are greater than or equal to T0 after being collected by the temperature sensor, and the predicted switching state changes, then the expression for T1 is as follows:

[0060]

[0061] Where T2 represents the temperature coefficient of the first bridge arm. If the temperatures of the two IGBTs in the second bridge arm are both less than T0 after being collected by the temperature sensor, or if the predicted switching state does not change, then T1 = 0. If the temperatures of the two IGBTs in the first bridge arm are both greater than or equal to T0 after being collected by the temperature sensor, and the predicted switching state changes, then the expression for T2 is as follows:

[0062]

[0063] Among them, T3 represents the temperature coefficient of the first bridge arm. If the temperatures of the two IGBTs in the first bridge arm are both less than T0 after being collected by the temperature sensor or the predicted switching state does not change, then T3 = 0. If the temperatures of the two IGBTs in the first bridge arm are both greater than or equal to T0 after being collected by the temperature sensor and the predicted switching state changes, then the expression of T3 is as follows:

[0064]

[0065] Step 1.7: Traverse the objective function 2 of the eight switching states, and select the minimum value of the objective function 2 as the switching state output at the current time, and send out the driving waveform.

[0066] Step 2: By collecting the temperature of the IGBT, construct a mathematical relationship to change the switching frequency of the IGBT, so as to reduce the heat generation of the IGBT and avoid damage to the IGBT;

[0067] Step 2.1: Collect the temperature values of the 6 IGBTs on the three-phase PWM rectifier through the temperature sensor; the temperature sensor uses a 46036 thermistor temperature sensor;

[0068] Step 2.2: Establish a frequency reduction function with the IGBT case temperature T as the independent variable as follows:

[0069]

[0070] Step 2.2: Establish a compensation frequency function with the rectifier DC voltage value v dc as the independent variable:

[0071]

[0072] is the DC side voltage given value of the three-phase PWM rectifier;

[0073] Step 2.3: Design the control of the driving waveform frequency output by the rectifier to the IGBT through the DSP control chip. The control steps are as follows:

[0074] Set the initial value of the frequency reduction parameter to 1. At the kth moment, collect the current six-way IGBT temperature value T. If the current temperature T < T0 and the output value of the frequency reduction function is 1, then set the frequency reduction parameter jp unchanged. If the value of the frequency reduction parameter jp is 1, the DSP does not perform additional processing, and it is default that the three-phase PWM rectifier works in the normal state;

[0075] If the current six-way TGBT temperature value T > T0, set the value of jp at the (K + 1)th moment of the frequency reduction parameter to 2. When the system initially works, the carrier frequency and the driving waveform frequency are the same and both are f. At this time, change the driving waveform frequency f at the current moment to the following frequency f0. At Within a given time period, the down-frequency parameter jp is set to 2. After a certain time, set the frequency reduction parameter value to 3:

[0076]

[0077] When the system JP value is 2, the DSP does not perform any additional processing. When the system JP value is 3, the DSP collects the IGBT temperature.

Claims

1. A single-vector temperature control frequency converter based on a three-phase PWM rectifier, characterized in that, It includes the following steps: Step 1: For a three-phase PWM rectifier, select the switching state by establishing an objective function for IGBT and power quality by utilizing the relationship between the AC-side voltages of the three-phase PWM rectifier. Step 2: By collecting the temperature of the IGBT, construct a mathematical relationship to change the switching frequency of the IGBT, thereby reducing the heat generation of the IGBT to avoid damage to the IGBT. Specifically, Step 1 is as follows: Step 1.1: Use the AC voltage sampling circuit in the control circuit to acquire the A, B, and C phase voltages of the three-phase PWM rectifier, and use the DC voltage sampling circuit in the control circuit to acquire the DC side voltage of the rectifier. The Hall current sampling circuit in the control circuit is used to collect the current of the three phases A, B, and C. Step 1.2: Establish a time-domain model of the rectifier according to Kirchhoff's voltage law, and obtain the following relationship through two-phase rotation transformation: Step 1.3: After transforming the formula described in Step 1.2 using the forward Euler method, obtain the current value in the two-phase stationary coordinate system at time k+1. , Specifically: Step 1.4: Establish calculation Compared with reference value The objective function 1 for the error is optimal, where the deviation between the predicted and actual values ​​is minimized when the objective function value is minimized. The objective function 1 is set as follows: Step 1.5: Traverse all switching states of the three-phase PWM rectifier. The three-phase PWM rectifier has eight switching states, therefore each predicted switching state corresponds to a different... , Therefore, this corresponds to the eight predictions. , Thus, the values ​​of eight objective functions F are obtained; Step 1.6: Collect the current temperature of the IGBT. If the warning temperature is set as T0 and the limit temperature is TMAX, and there are 6 IGBTs in the three-phase PWM rectifier. If the temperatures of all 6 IGBTs are lower than the warning temperature T0, then select the switching sequence corresponding to the minimum value of the objective function F set in Step 1.4 as the switching state at the current moment and output it to... If the temperature of any IGBT among the 6 IGBTs exceeds T0, then establish the following objective function 2: Step 1.7: Traverse the objective function 2 of the eight switching states, and select the minimum value of the objective function 2 as the switching state output at the current time and issue a drive waveform. In step 1.2 , , , The grid-side current and voltage in the three-phase stationary coordinate system are converted into grid-side current and voltage in the two-phase stationary coordinate system, respectively. , To convert AC voltage measurement to AC voltage measurement in a two-phase stationary coordinate system, R is the grid-side equivalent resistance and L is the grid-side inductance; In step 1.3 , , , , , for , , , , , The value at time k, , for , The value at time k+1; In step 1.4 , The active current weighting factor and reactive current weighting factor are given by humans, where for The shaft predicted current value, where for Shaft predicted current value, using DC side reference value DC side voltage of three-phase PWM rectifier The difference is processed through a PI circuit, and the resulting value is compared with 0 by rotating the two phases to the two-phase stationary coordinate system after the two-phase stationary coordinate transformation. Shaft Predicted Current Value , Shaft Predicted Current Value ; In step 1.6 This is expressed as the temperature coefficient of the first bridge arm. If the temperatures of both IGBTs in the first bridge arm, as measured by the temperature sensor, are both less than T0, or if the predicted switching state remains unchanged, then... =0, if the temperatures of both IGBTs in the first bridge arm are greater than or equal to T0 after being collected by the temperature sensor, and the predicted switching state changes, then The expression is as follows: in This is represented as the temperature coefficient of the first bridge arm. If the temperatures of both IGBTs in the second bridge arm, as measured by the temperature sensor, are both less than T0, or if the predicted switching state remains unchanged, then... =0, if the temperatures of both IGBTs in the first bridge arm are greater than or equal to T0 after being collected by the temperature sensor, and the pre-set switching state changes, then The expression is as follows: in This is expressed as the temperature coefficient of the first bridge arm. If the temperatures of both IGBTs in the first bridge arm, as measured by the temperature sensor, are both less than T0, or if the predicted switching state remains unchanged, then... =0, if the temperatures of both IGBTs in the first bridge arm are greater than or equal to T0 after being collected by the temperature sensor, and the pre-set switching state changes, then The expression is as follows: 。 2. The single-vector temperature control frequency converter method based on a three-phase PWM rectifier according to claim 1, characterized in that, Specifically, Step 2 is as follows: Step 2.1: Collect the temperature values of the 6 IGBTs on the three-phase PWM rectifier through temperature sensors. Step 2.2: Establish a frequency reduction function with the IGBT case temperature T as the independent variable as follows: Step 2.2: Establish the DC voltage value of the rectifier The compensation frequency function for the independent variable: Vdc* is the given value of the DC-side voltage of the three-phase PWM rectifier. Step 2.3: Design the control of the frequency of the drive waveform output from the rectifier to the IGBT through a DSP control chip. The control steps are as follows: Set the initial value of the frequency reduction parameter as 1. At the k-th moment, collect the current temperature values T of the six IGBTs. If the current temperature T < the output value of the frequency reduction function is 1, then set the frequency reduction parameter jp unchanged. If the value of the frequency reduction parameter jp is 1, then the DSP does not perform additional processing and defaults that the three-phase PWM rectifier operates in a normal state. If the current temperature value T of the six TGBT channels is greater than T0, and the jp value of the frequency reduction parameter is set to 2 at time K+1, the carrier frequency and the drive waveform frequency are the same when the system initially starts working. At this time, the driving waveform frequency will be... Change to the following frequency ,exist Within a given time period, the down-frequency parameter jp is set to 2. After a certain time, set the frequency reduction parameter value to 3: When the system jp value is 2, the DSP does not perform additional processing. When the system jp value is 3, the DSP collects the temperature of the IGBT. When the temperature T < T0, the jp value is set to 1, and the driving waveform frequency is set to .

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