A three-level dc transformer neutral point potential control loop, method and system

Abstract

The application discloses a three-level DC transformer neutral point potential control loop, method and system, the method comprises the following steps: acquiring capacitor voltages U C1 、 U C2 、 U C3 on both sides of C1, C2 and C3 C3 ; taking the difference between U C1 and a preset voltage value as input, outputting an external phase angle through a PI controller; inputting the difference between U C2 into the PI controller, and calculating the duty cycles of Q1 and Q4 according to the positive and negative relationship of the external phase angle; inputting the duty cycles of Q1 and Q4 and the external phase angle into a preset pulse generator module to obtain trigger pulse signals of all switch tubes; and transmitting the trigger pulse signals to the switch tubes to realize neutral point potential control of the three-level DC transformer. The application can effectively adjust the neutral point potential under no-load, light-load and full-load conditions, and solves the problem that the neutral point potential control effect of the transformer is poor under no-load or light-load.

Description

Technical Field

[0001] This invention relates to a control circuit, method, and system for the neutral point potential of a three-level DC transformer, belonging to the field of DC transformer technology. Background Technology

[0002] Currently, due to the limited voltage withstand ratings of power electronic switching devices, they cannot meet the requirements of high-power, high-voltage applications. Therefore, multi-level circuits are often used to meet the high-voltage requirements, with three-level topologies being the most widely used. Three-level topologies have two capacitors connected in series on the DC bus side. Due to non-ideal factors in the circuit, differences in component parameters, or the inherent characteristics of the modulation method, the voltages of the two capacitors often deviate, causing an imbalance in the midpoint potential. This ultimately leads to distortion of the output voltage and even damage to components. Therefore, appropriate methods must be adopted to suppress the deviation of the midpoint potential.

[0003] For a single-phase three-level DC transformer, the most intuitive idea is to adjust the conduction time of the upper and lower bridge arms, i.e., the charging and discharging time of the two capacitors, to balance the neutral point potential. However, this method is not very effective under no-load and light-load conditions, especially when there is a resonant capacitor in the circuit. Another method is to add a flying capacitor to give the capacitor voltage self-balancing capability, but this is not suitable for reverse power transfer conditions. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a neutral point potential control circuit, method and system for a three-level DC transformer, which solves the problem of poor neutral point potential control effect of transformers under no-load or light-load conditions.

[0005] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0006] In a first aspect, the present invention provides a three-level DC transformer neutral point potential control circuit, comprising: a master module, a slave module, and an isolation transformer module, wherein:

[0007] The host module includes two bus capacitors C1 and C2 and six switching transistors Q1 to Q6. The bus capacitors C1 and C2 are connected to the positive and negative DC buses respectively. The connection point of the bus capacitors C1 and C2 is the neutral point N. Q1 and Q2 form the upper bridge arm, Q3 and Q4 form the lower bridge arm, Q5 and Q6 are connected to the anodes of Q2 and Q4 respectively, and the cathode of Q5 is connected to the anode of Q6 and connected to the midpoint N.

[0008] The slave module includes four switching transistors S1 to S4 and a capacitor C3. The two ends of the capacitor C3 are connected to the positive and negative busbars respectively. The four switching transistors S1 to S4 form an H-bridge. S1 and S2 are connected in series and then in parallel with S3 and S4, and then in parallel with the capacitor C3.

[0009] The isolation transformer module includes a high-frequency transformer T, which has a parasitic inductance L. The primary side of the high-frequency transformer T is connected to the cathode of Q2 and the midpoint N, respectively, and the secondary side is connected to the cathodes of S1 and S3, respectively.

[0010] Secondly, the present invention provides a control method based on the aforementioned three-level DC transformer neutral point potential control circuit, comprising:

[0011] Obtain the capacitor voltage U across C1, C2, and C3. C1 U C2 U C3 ;

[0012] Will U C3 The difference between the voltage value and the preset voltage value is used as input, and the output of the PI controller is used to obtain the outward phase shift angle.

[0013] The U C1 U C2 The difference is input to the PI controller, and the duty cycles of Q1 and Q4 are calculated based on the positive and negative relationship of the external phase angle.

[0014] The duty cycles and outward phase shift angles of Q1 and Q4 are input into a preset pulse generator module to obtain trigger pulse signals for all switching transistors.

[0015] The trigger pulse signal is transmitted to each switching transistor to achieve midpoint potential control of the three-level DC transformer.

[0016] Furthermore, a first-order Kalman filter is used to filter the capacitor voltage U. C1 U C2 U C3 The filtering is performed using the outward phase shift angle, and the calculation formula is as follows:

[0017] x k =Fx k-1

[0018] P k =FP k-1 F T +Q k

[0019] K k =P k H k T (H k P k H k T +R k ) -1

[0020] x k '=x k +K k (z k -H k x k )

[0021] P k '=P k -K k H k P k

[0022] In the formula x k Let P be the state vector at time k, F be the state transition matrix, and P be the state vector at time k. k Let Q be the covariance matrix of the state vector. k Let K be the noise covariance matrix. k For Kalman gain, R k Let x be the sensor noise covariance matrix. k ' is the optimal estimate of the state vector, z k For sensor observations, P k ' is the optimal covariance matrix, capacitor voltage U C1 U C2 U C3 The outward phase shift angle is used as the filter input, corresponding to z in the formula. k x k 'This is the output result after filtering both.

[0023] Furthermore, the U C3 The difference between the voltage value and the preset voltage value is used as input, and the output of the PI controller is used to obtain the external phase shift angle. The calculation formula is as follows:

[0024]

[0025] In the formula, DAB_EXT is the external phase shift angle, Uset is the preset voltage value, PI is the parameter of the PI regulator, and s is the integral sign.

[0026] Furthermore, the U C1 U C2 The difference is input to the PI controller, and the duty cycles of Q1 and Q4 are calculated based on the sign relationship of the outer phase shift angle, including:

[0027] If the outward phase shift is positive, the duty cycles of Q1 and Q4 are respectively:

[0028]

[0029]

[0030] If the outward shift angle is negative, then the duty cycles of Q1 and Q4 are respectively:

[0031]

[0032]

[0033] In the formula, ΔU is U C1 and U C2 The difference, ΔU=U C1 -U C2 D1D4 represents the duty cycle of Q1Q4, with a value range of [0.5-DAB_EXT / 180,0.5]. PI is the parameter of the PI controller, and s is the integral sign.

[0034] Furthermore, the duty cycles and outward phase shift angles of Q1 and Q4 are input into a preset pulse generator module to obtain trigger pulse signals for all switching transistors, including:

[0035] The duty cycles and outward phase shift angles of Q1 and Q4 are input into a preset pulse generator module. Since the trigger pulses of Q1 and Q3 are complementary, the trigger pulses of Q2 and Q4 are complementary, the trigger pulses of Q5 and Q3 are the same, the trigger pulses of Q6 and Q2 are the same, S1 lags Q1 DAB_EXT / 360×T, the trigger pulses of S1 and S2 are complementary, the trigger pulses of S1 and S4 are the same, and the trigger pulses of S3 and S4 are complementary, thus obtaining the trigger pulse signals of all switching transistors.

[0036] Thirdly, the present invention provides a control system based on the aforementioned three-level DC transformer midpoint potential control circuit, comprising:

[0037] The capacitor voltage acquisition module is used to acquire the capacitor voltage U across capacitors C1, C2, and C3. C1 U C2 U C3 ;

[0038] The outer phase angle calculation module is used to calculate U C3 The difference between the voltage value and the preset voltage value is used as input, and the output of the PI controller is used to obtain the outward phase shift angle.

[0039] The duty cycle calculation module is used to calculate the U C1 U C2 The difference is input to the PI controller, and the duty cycles of Q1 and Q4 are calculated based on the positive and negative relationship of the external phase angle.

[0040] The pulse signal generation module is used to input the duty cycle and outward phase shift angle of Q1 and Q4 into a preset pulse generator module to obtain the trigger pulse signals of all switching transistors;

[0041] The communication module is used to transmit the trigger pulse signal to each switching transistor to realize the midpoint potential control of the three-level DC transformer.

[0042] Furthermore, it also includes a filtering module for using a first-order Kalman filter to filter the capacitor voltage U. C1 U C2 U C3 The filtering is performed using the outward phase shift angle, and the calculation formula is as follows:

[0043] x k =Fx k-1

[0044] P k =FP k-1 F T +Q k

[0045] K k =P k H k T (H k P k H k T +R k ) -1

[0046] x k '=x k +K k (z k -H k x k )

[0047] P k '=P k -K k H k P k

[0048] In the formula x k Let P be the state vector at time k, F be the state transition matrix, and P be the state vector at time k. k Let Q be the covariance matrix of the state vector. k Let K be the noise covariance matrix. k For Kalman gain, R k Let x be the sensor noise covariance matrix. k ' represents the optimal estimate of the state vector, zk represents the sensor observations, Pk' represents the optimal covariance matrix, and U represents the capacitor voltage. C1 U C2 U C3 The outward phase shift angle is used as the filter input, corresponding to z in the formula. k x k 'This is the output result after filtering both.

[0049] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0050] 1. This invention can effectively regulate the neutral point potential under no-load, light-load, and full-load conditions; 2. The switching transistors in this invention are all turned on at zero voltage, which greatly reduces the turn-on loss; 3. This invention uses Kalman filtering to filter the voltage and outward phase shift angle, which can prevent frequent and repeated adjustments caused by voltage and outward phase shift angle fluctuations. Attached Figure Description

[0051] Figure 1 This is a structural diagram of a three-level DC transformer midpoint potential control circuit provided in an embodiment of the present invention;

[0052] Figure 2 This is a schematic diagram of the control pulse waveform provided in an embodiment of the present invention;

[0053] Figure 3 This is a schematic diagram of the host control pulse generator provided in an embodiment of the present invention;

[0054] Figure 4 This is a schematic diagram of a slave control pulse generator provided in an embodiment of the present invention;

[0055] Figure 5 This is a schematic diagram of the voltage regulation control module provided in an embodiment of the present invention;

[0056] Figure 6 This is a schematic diagram of the pressure equalization control module provided in an embodiment of the present invention;

[0057] Figure 7 This is a schematic diagram of the filtering module provided in an embodiment of the present invention. Detailed Implementation

[0058] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0059] Example 1

[0060] like Figure 1 As shown, this embodiment introduces a three-level DC transformer neutral point potential control circuit, including: a master module, a slave module, and an isolation transformer module, wherein:

[0061] The host module includes two bus capacitors C1 and C2 and six switching transistors Q1 to Q6. The bus capacitors C1 and C2 are connected to the positive and negative DC buses respectively. The connection point of the bus capacitors C1 and C2 is the neutral point N. Q1 and Q2 form the upper bridge arm, Q3 and Q4 form the lower bridge arm, Q5 and Q6 are connected to the anodes of Q2 and Q4 respectively, and the cathode of Q5 is connected to the anode of Q6 and connected to the midpoint N.

[0062] The slave module includes four switching transistors S1 to S4 and a capacitor C3. The two ends of the capacitor C3 are connected to the positive and negative busbars respectively. The four switching transistors S1 to S4 form an H-bridge. S1 and S2 are connected in series and then in parallel with S3 and S4, and then in parallel with the capacitor C3.

[0063] The isolation transformer module includes a high-frequency transformer T, which has a parasitic inductance L. The primary side of the high-frequency transformer T is connected to the cathode of Q2 and the midpoint N, respectively, and the secondary side is connected to the cathodes of S1 and S3, respectively.

[0064] Example 2

[0065] This embodiment provides a control method for the neutral point potential control circuit of a three-level DC transformer according to Embodiment 1, including:

[0066] Obtain the capacitor voltage U across C1, C2, and C3. C1 U C2 U C3 ;

[0067] Will U C3 The difference between the voltage value and the preset voltage value is used as input, and the output of the PI controller is used to obtain the outward phase shift angle.

[0068] The U C1 U C2 The difference is input to the PI controller, and the duty cycles of Q1 and Q4 are calculated based on the positive and negative relationship of the external phase angle.

[0069] The duty cycles and outward phase shift angles of Q1 and Q4 are input into a preset pulse generator module to obtain trigger pulse signals for all switching transistors.

[0070] The trigger pulse signal is transmitted to each switching transistor to achieve midpoint potential control of the three-level DC transformer.

[0071] The application process of the three-level DC transformer neutral point potential control circuit provided in this embodiment involves the following steps:

[0072] (1) Signal acquisition and filtering

[0073] This section collects the capacitor voltage, including U. C1U C2 U C3 The phase shift angle, and a first-order Kalman filter are used for filtering, calculated as follows:

[0074] x k =Fx k-1

[0075] P k =FP k-1 F T +Q k

[0076] K k =P k H k T (H k P k H k T +R k ) -1

[0077] x k '=x k +K k (z k -H k x k )

[0078] P k '=P k -K k H k P k

[0079] In the formula, xk is the state vector at time k, F is the state transition matrix, Pk is the covariance matrix of the state vector, and Q... k Let K be the noise covariance matrix. k Let H be the Kalman gain, H be the transformation matrix, and R be the Kalman gain. k Let x be the sensor noise covariance matrix. k ' is the optimal estimate of the state vector, z k For sensor observations, Pk' is the optimal covariance matrix, zk is the filter input, and xk' is the filtered output.

[0080] For the above parameters, the initialization parameters can be selected as F=1, Q=0.002, R=0.05, and H=1 in this system.

[0081] (2) Calculation of external phase angle

[0082] The filtered low-voltage side voltage, i.e., U C3 The difference between the input and the preset value is used as input, and the output of the PI control module is the outward phase shift angle DAB_EXT. The calculation block diagram is as follows. Figure 5 As shown.

[0083]

[0084] In the formula, UL is the low-voltage side voltage, Uset is the preset voltage value, PI is the parameter of the PI regulator, and s is the integral sign.

[0085] (2) Duty cycle calculation

[0086] The filtered capacitor voltage U C1 UC2, input PI controller, see Figure 6 Then the duty cycle D1D2 of Q1Q4 can be calculated, and the sign of the filtered outward phase shift angle can be determined. If the outward phase shift angle is positive...

[0087]

[0088]

[0089] If the outward shift angle is negative, then the duty cycles of Q1 and Q4 are respectively:

[0090]

[0091]

[0092] In the formula, ΔU is U C1 and U C2 The difference, ΔU=U C1 -U C2 D1D4 represents the duty cycle of Q1Q4, with a value range of [0.5-DAB_EXT / 180,0.5]. PI is the parameter of the PI controller, and s is the integral sign.

[0093] (3) Control pulse modulation

[0094] The duty cycles of Q1 and Q4 and the external phase shift angle are calculated for the input pulse generator module. Since the trigger pulses of Q1 and Q3 are complementary, the trigger pulses of Q2 and Q4 are complementary, the trigger pulses of Q5 and Q3 are the same, the trigger pulses of Q6 and Q2 are the same, S1 lags Q1 (DAB_EXT / 360×T), the trigger pulses of S1 and S2 are complementary, the trigger pulses of S1 and S4 are the same, and the trigger pulses of S3 and S4 are complementary, thus the trigger pulse signals for all switching transistors are obtained. The pulse generator is as follows: Figure 3 Figure 4 As shown, the trigger pulse is as follows Figure 2 As shown.

[0095] (4) Finally, the pulse signal is transmitted to each switch in the main circuit, so that the midpoint potential control of the three-level DC transformer can be realized.

[0096] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A control method for a neutral point potential control circuit of a three-level DC transformer, characterized in that, The control loop includes: a master module, a slave module, and an isolation transformer module, wherein: The host module includes two bus capacitors C1 and C2 and six switching transistors Q1 to Q6. The bus capacitors C1 and C2 are connected to the positive and negative DC buses respectively. The connection point of the bus capacitors C1 and C2 is the neutral point N. Q1 and Q2 form the upper bridge arm, Q3 and Q4 form the lower bridge arm, Q5 and Q6 are connected to the anodes of Q2 and Q4 respectively, and the cathode of Q5 is connected to the anode of Q6 and connected to the midpoint N. The slave module includes four switching transistors S1 to S4 and a capacitor C3. The two ends of the capacitor C3 are connected to the positive and negative busbars respectively. The four insulated gate bipolar transistors S1 to S4 form an H-bridge. S1 and S2 are connected in series and then in parallel with S3 and S4, and then in parallel with the capacitor C3. The isolation transformer module includes a high-frequency transformer T, which has a parasitic inductance L. The primary side of the high-frequency transformer T is connected to the cathode of Q2 and the midpoint N, respectively, and the secondary side is connected to the cathodes of S1 and S3, respectively. The control method includes: Obtain the capacitor voltage U across C1, C2, and C3. C1 U C2 U C3 ; Will U C3 The difference between the voltage value and the preset voltage value is used as input, and the output of the PI controller is used to obtain the outward phase shift angle. The U C1 U C2 The difference is input to the PI controller, and the duty cycles of Q1 and Q4 are calculated based on the sign relationship of the outer phase shift angle; including: If the outward phase shift is positive, the duty cycles of Q1 and Q4 are respectively: If the outward shift angle is negative, then the duty cycles of Q1 and Q4 are respectively: In the formula, ΔU is U C1 and U C2 The difference, ΔU=U C1 -U C2 D1 and D4 represent the duty cycles of Q1 and Q4, with values ​​ranging from [0.5-DAB_EXT / 180, 0.5]. P and I are the parameters of the PI controller, and s is the integral sign. The duty cycles and outward phase shift angles of Q1 and Q4 are input into a preset pulse generator module to obtain trigger pulse signals for all switching transistors. The trigger pulse signal is transmitted to each switching transistor to achieve midpoint potential control of the three-level DC transformer.

2. The control method for the neutral point potential control circuit of a three-level DC transformer according to claim 1, characterized in that, A first-order Kalman filter is used to filter the capacitor voltage U. C1 U C2 U C3 The filtering is performed using the outward phase shift angle, and the calculation formula is as follows: x k =Fx k-1 P k =FP k-1 F T +Q k K k =P k H k T (H k P k H k T +R k ) -1 x k '=x k +K k (z k -H k x k ) P k '=P k -K k H k P k In the formula x k Let P be the state vector at time k, F be the state transition matrix, and P be the state vector at time k. k Let Q be the covariance matrix of the state vector. k Let K be the noise covariance matrix. k For Kalman gain, R k Let x be the sensor noise covariance matrix. k ' is the optimal estimate of the state vector, z k For sensor observations, P k ' is the optimal covariance matrix, capacitor voltage U C1 U C2 U C3 The outward phase shift angle is used as the filter input, corresponding to z in the formula. k x k 'This is the output result after filtering both.

3. The control method for the neutral point potential control circuit of a three-level DC transformer according to claim 1, characterized in that, The U C3 The difference between the voltage value and the preset voltage value is used as input, and the output of the PI controller is used to obtain the external phase shift angle. The calculation formula is as follows: In the formula, DAB_EXT is the external phase shift angle, Uset is the preset voltage value, P and I are the parameters of the PI controller, and s is the integral sign.

4. The control method for the neutral point potential control circuit of a three-level DC transformer according to claim 1, characterized in that, The duty cycles and outward phase shift angles of Q1 and Q4 are input into a preset pulse generator module to obtain trigger pulse signals for all switching transistors, including: The duty cycles and outward phase shift angles of Q1 and Q4 are input into a preset pulse generator module. Since the trigger pulses of Q1 and Q3 are complementary, the trigger pulses of Q2 and Q4 are complementary, the trigger pulses of Q5 and Q3 are the same, the trigger pulses of Q6 and Q2 are the same, S1 lags Q1 DAB_EXT / 360×T, the trigger pulses of S1 and S2 are complementary, the trigger pulses of S1 and S4 are the same, and the trigger pulses of S3 and S4 are complementary, thus obtaining the trigger pulse signals of all switching transistors.

5. A control system for the neutral point potential control circuit of a three-level DC transformer according to claim 1, characterized in that, include: The capacitor voltage acquisition module is used to acquire the capacitor voltage U across capacitors C1, C2, and C3. C1 U C2 U C3 ; The outer phase angle calculation module is used to calculate U C3 The difference between the voltage value and the preset voltage value is used as input, and the output of the PI controller is used to obtain the outward phase shift angle. The duty cycle calculation module is used to calculate the U C1 U C2 The difference is input to the PI controller, and the duty cycles of Q1 and Q4 are calculated based on the positive and negative relationship of the external phase angle. The pulse signal generation module is used to input the duty cycle and outward phase shift angle of Q1 and Q4 into a preset pulse generator module to obtain the trigger pulse signals of all switching transistors; The communication module is used to transmit the trigger pulse signal to each switching transistor to realize the midpoint potential control of the three-level DC transformer.

6. The control system for the three-level DC transformer neutral point potential control circuit according to claim 5, characterized in that, It also includes a filtering module for using a first-order Kalman filter to filter the capacitor voltage U. C1 U C2 U C3 The filtering is performed using the outward phase shift angle, and the calculation formula is as follows: x k =Fx k-1 P k =FP k-1 F T +Q k K k =P k H k T (H k P k H k T +R k ) -1 x k '=x k +K k (z k -H k x k ) P k '=P k -K k H k P k In the formula x k Let P be the state vector at time k, F be the state transition matrix, and P be the state vector at time k. k Let Q be the covariance matrix of the state vector. k Let K be the noise covariance matrix. k For Kalman gain, R k Let x be the sensor noise covariance matrix. k ' is the optimal estimate of the state vector, z k For sensor observations, P k ' is the optimal covariance matrix, capacitor voltage U C1 U C2 U C3 The outward phase shift angle is used as the filter input, corresponding to z in the formula. k x k 'This is the output result after filtering both.

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