Power quality compensation device and control method thereof

Abstract

The present disclosure provides a power quality compensation device and a control method thereof. The power quality compensation device is electrically connected to a power grid and a non-linear load, and includes a current controller, a converter, a ripple predictor, a processing unit, and a voltage controller. The current controller receives an instruction current and outputs a switching control signal. The converter outputs an output current and an actual DC bus voltage according to the switching control signal. The ripple predictor receives an intermediate voltage and a first current and outputs a predicted ripple voltage, wherein the intermediate voltage is a voltage at a common connection point between the power grid and the non-linear load. The processing unit outputs a processing result according to the actual DC bus voltage, the predicted ripple voltage, and a reference DC bus voltage. The voltage controller receives the processing result and outputs a voltage control signal to the current controller.

Description

Technical Field

[0001] This disclosure relates to a power quality compensation device and its control method, and in particular to a power quality compensation device and its control method that can compensate for harmonics and reactive current in the power grid. Background Technology

[0002] In various electricity consumption sectors, as the number of nonlinear loads connected to the power grid increases, the harmonics and reactive power generated by these loads will affect power quality and consequently damage electrical equipment in the grid. Current technologies often utilize active power filters (APFs) or static var generators (SVGs) to compensate for the harmonics and reactive power generated by nonlinear loads in the power grid, thereby improving power quality.

[0003] Generally, APF / SVG improves the quality of the final current flowing into the power grid by extracting harmonic and reactive components from the load current and generating a current of equal magnitude but opposite direction. To better compensate for harmonics and reactive current, APF / SVG typically employs a dual-loop control method with an outer voltage loop and an inner current loop. The inner current loop tracks the commanded current, while the outer voltage loop ensures the average bus voltage is stabilized within a specific range. To ensure the stability of the average bus voltage, sampling and low-pass filtering are usually performed, and a relatively low voltage loop bandwidth is designed. This leads to problems such as slow voltage loop response, large bus voltage fluctuations, and bus voltage fluctuations exceeding protection limits.

[0004] Therefore, developing a power quality compensation device and its control method that can improve the existing technology is an urgent need at present. Summary of the Invention

[0005] The purpose of this disclosure is to provide a power quality compensation device and its control method, which predicts the ripple in the bus voltage and compensates for the power quality accordingly. This improves the response speed of the bus voltage loop and enables optimized control of the bus voltage.

[0006] To achieve the above objectives, this disclosure provides a power quality compensation device electrically connected to a power grid and a nonlinear load, and includes a current controller, a converter, a ripple predictor, a processing unit, and a voltage controller. The current controller receives a command current and outputs a switching control signal. The converter is electrically coupled to the current controller and outputs an output current and the actual DC bus voltage according to the switching control signal. The ripple predictor receives an intermediate voltage and a first current and outputs a predicted ripple voltage, wherein the intermediate voltage is the voltage at the common connection point between the power grid and the nonlinear load. The processing unit is electrically connected to the ripple predictor and the converter and outputs a processing result based on the actual DC bus voltage, the predicted ripple voltage, and a reference DC bus voltage. The voltage controller is electrically coupled between the processing unit and the current controller, receives the processing result, and outputs a voltage control signal to the current controller.

[0007] To achieve the above objectives, this disclosure provides a control method applicable to a power quality compensation device electrically connected to a power grid and a nonlinear load. The control method includes: receiving a command current and outputting a switching control signal using a current controller; outputting an output current and an actual DC bus voltage using a converter based on the switching control signal; outputting a predicted ripple voltage using a ripple predictor based on an intermediate voltage and a first current, wherein the intermediate voltage is the voltage at the common connection point between the power grid and the nonlinear load; outputting a processing result using a processing unit based on the actual DC bus voltage, the predicted ripple voltage, and a reference DC bus voltage; and outputting a voltage control signal to the current controller using a voltage controller based on the processing result.

[0008] This disclosure provides a power quality compensation device and its control method. When compensating for harmonics and reactive power generated by nonlinear loads in the power grid, the power quality device predicts the ripple component of the bus voltage based on the voltage and first current at the common connection point between the power grid and the nonlinear load. This prediction is then canceled out with the ripple component of the sampled actual DC bus voltage to obtain the DC component of the DC bus voltage. The power quality compensation device 1a of this disclosure employs a high-bandwidth voltage control loop, improving the response speed of the voltage loop and achieving optimized control of the bus voltage, thereby improving the stability of the device and the power quality management effect. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the power quality compensation device according to the first embodiment of this disclosure.

[0010] Figure 2 This is a schematic diagram of the power quality compensation device according to the second embodiment of this disclosure.

[0011] Figure 3 This is a schematic diagram of the power quality compensation device according to the third embodiment of this disclosure.

[0012] Figure 4 This is a schematic diagram of the power quality compensation device according to the fourth embodiment of this disclosure.

[0013] Figure 5 This is a schematic diagram of the steps of a control method according to a preferred embodiment of the present disclosure.

[0014] The reference numerals in the attached figures are explained as follows:

[0015] 1a, 1b, 1c, 1d: Power quality compensation devices

[0016] 2: Power Grid

[0017] 3: Nonlinear load

[0018] 11: Current Controller

[0019] 12: Converter

[0020] 13a, 13b: Ripple predictor

[0021] 14: Processing Unit

[0022] 141: Arithmetic Unit

[0023] 142: Comparator

[0024] 15: Voltage Controller

[0025] 16: Drive circuit

[0026] 17a, 17b: Detectors

[0027] i o Output current

[0028] u dc Actual DC bus voltage

[0029] u pcc Intermediate voltage

[0030] u dc_ripple Predicting ripple voltage

[0031] u dc_ref Reference DC bus voltage

[0032] i L Nonlinear load current

[0033] i s : Grid current

[0034] S1, S2, S3, S4, S5: Steps Detailed Implementation

[0035] Some typical embodiments embodying the features and advantages of this disclosure will be described in detail in the following description. It should be understood that this disclosure can be varied in different implementations without departing from the scope of this disclosure, and the descriptions and drawings therein are for illustrative purposes only and not intended to limit this disclosure.

[0036] Figure 1 This is a schematic diagram of the power quality compensation device according to the first embodiment of this disclosure. Figure 1 As shown, the power quality compensation device 1a is electrically connected to the power grid 2 and the nonlinear load 3. The power quality compensation device 1a includes a current controller 11, a converter 12, a ripple predictor 13a, a processing unit 14, and a voltage controller 15. The power quality compensation device 1a can be, for example, but not limited to, an active power filter, a static var generator (SVA), or an enhanced SVA with harmonic compensation. The current controller 11 receives a command current and outputs a switching control signal. The converter 12 is electrically coupled to the current controller 11 and receives the switching control signal. The converter 12 is used to output an output current i according to the switching control signal. o and actual DC bus voltage u dc Ripple predictor 13a receives intermediate voltage u. pcc And the first current, and based on this, output the predicted ripple voltage u. dc_ripple The intermediate voltage u pcc The voltage at the common connection point between the power grid 2 and the nonlinear load 3 is denoted as u. The processing unit 14 is electrically connected to the ripple predictor 13a and the converter 12 to receive the predicted ripple voltage u. dc_ripple and actual DC bus voltage u dc The processing unit 14 also receives the reference DC bus voltage u. dc_ref The processing unit 14 determines the actual DC bus voltage u based on the actual DC bus voltage u. dc Predicted ripple voltage u dc_ripple and reference DC bus voltage u dc_ref The output processing result is then processed. Voltage controller 15 is electrically coupled between processing unit 14 and current controller 11. Voltage controller 15 receives the processing result and outputs a voltage control signal to current controller 11. Ripple predictor 13a determines the ripple based on the intermediate voltage u at the common connection point between power grid 2 and nonlinear load 3. pcc The first current is used to predict the harmonics generated by the nonlinear load 3 and the ripple generated by the bus voltage during reactive power in the power quality compensation device 1a in the power grid 2. The predicted ripple voltage u is... dc_ripple Reflects the actual DC bus voltage u dc The ripple component in the actual DC bus voltage u is removed by the processing unit 14. dc With reference DC bus voltage u dc_refThe output processing result is compared to the output result, so that the voltage controller 15 and the current controller 11 can control the operation of the converter 12 accordingly. In this way, the power quality compensation device 1a of this disclosure adopts a high-bandwidth voltage control loop, which improves the voltage loop response speed, realizes optimized control of the bus voltage, and thus improves the stability of the device and the power quality management effect.

[0037] The following example illustrates a specific implementation of the ripple predictor of this disclosure. The bus capacitance is C, and the first current is i. o The initial bus capacitor voltage is U0. After a period of time t, due to energy exchange between the power quality compensation device and grid 2, the bus capacitor voltage becomes U0 + ΔU, where ΔU is the bus ripple. According to the law of conservation of energy, the following equation can be obtained:

[0038]

[0039] After simplification, we get:

[0040]

[0041] Since the change in ΔU is small, the aforementioned equation can be used to approximate the bus ripple ΔU:

[0042]

[0043] In some embodiments, the processing unit 14 includes an arithmetic unit 141 and a comparator 142. The arithmetic unit 141 is electrically connected to the ripple predictor 13a and the converter 12 to receive the actual DC bus voltage u. dc and predicted ripple voltage u dc_ripple And output the actual DC bus voltage u through calculation. dc With predicted ripple voltage u dc_ripple The difference between the two values. Comparator 142 is electrically connected between the arithmetic unit 141 and the voltage controller 15. Comparator 142 receives this difference and compares it with the reference DC bus voltage u. dc_ref The comparison yields the processing result. In some embodiments, the power quality compensation device 1a further includes a drive circuit 16. The drive circuit 16 is electrically connected between the current controller 11 and the converter 12. The drive circuit 16 receives the switching control signal output by the current controller 11 and outputs a drive signal to the converter 12 according to the switching control signal. The converter 12 operates according to the drive signal.

[0044] In addition, Figure 1 and Figure 3 In the first and third embodiments shown, the first current is the output current i o The ripple predictor 13a of the power quality compensation device 1a is based on the intermediate voltage u pcc and output current io Output predicted ripple voltage u dc_ripple However, in other embodiments, for example... Figure 2 and Figure 4 In the second and fourth embodiments shown, the first current can also be a command current, and the ripple predictor 13b of the power quality compensation device 1b predicts the ripple current based on the intermediate voltage u. pcc and command current output predicted ripple voltage u dc_ripple .

[0045] Furthermore, at Figure 1 and Figure 2 In the first and second embodiments shown, the command current is the nonlinear load current i L The reference current. However, in other embodiments, such as Figure 3 and Figure 4 In the third and fourth embodiments shown, the command current is the grid current i. s The reference current, where Figure 3 and Figure 4 The first current is shown as the output current i. o Different implementations of command current. Figure 2 , Figure 3 and Figure 4 Zhongyu Figure 1 Components marked with the same symbol have similar structures and functions, and will not be described further here.

[0046] In addition, Figure 1 and Figure 2 In the first and second embodiments shown, the power quality compensation devices 1a and 1b further include a detector 17a, which is electrically connected to the current controller 11 and is used to detect the nonlinear load current i. L The detector 17a outputs a command current to the current controller 11 based on the detection results of the fundamental positive-sequence component, fundamental negative-sequence component, fundamental zero-sequence component, and harmonic components. Figure 3 and Figure 4 In the third and fourth embodiments shown, the power quality compensation devices 1c and 1d further include a detector 17b, which is electrically connected to the current controller 11 and is used to detect the grid current i. s The detector 17b outputs a command current to the current controller 11 based on the detection results of the fundamental positive sequence component, fundamental negative sequence component, fundamental zero sequence component and harmonic components.

[0047] Figure 5 This diagram illustrates the steps of a control method according to a preferred embodiment of the present disclosure. This control method is applicable to the power quality compensation devices in the foregoing embodiments. Figure 5 As shown, the control method includes:

[0048] Step S1: Receive the command current and output the switch control signal using the current controller 11;

[0049] Step S2: The converter 12 outputs the output current i according to the switch control signal. o and actual DC bus voltage u dc ;

[0050] Step S3, using ripple predictor 13a or 13b based on the intermediate voltage u pcc and the first current output predicted ripple voltage u dc_ripple The intermediate voltage u pcc The voltage at the common connection point between power grid 2 and nonlinear load 3;

[0051] Step S4, using processing unit 14 to determine the actual DC bus voltage u dc Predicted ripple voltage u dc_ripple and reference DC bus voltage u dc_ref Output processing results; and

[0052] Step S5: The voltage controller 15 outputs a voltage control signal to the current controller 11 based on the processing result.

[0053] It should be noted that steps S1 to S5 can be executed cyclically, and any step can be used as the starting step when executing the control method.

[0054] In some embodiments, the control method further includes the step of: using the drive circuit 16 to receive and output a drive signal to the converter 12 according to the switch control signal output by the current controller 11, wherein the converter 12 operates according to the drive signal.

[0055] In this control method, the first current can be the output current i. o Or command current, where the command current can be the grid current i s or nonlinear load current i L The reference current. Furthermore, when the control method is used to control... Figure 1 and Figure 2 When using the power quality compensation devices 1a and 1b shown, the control method further includes the step of: detecting the nonlinear load current i using detector 17a. L The fundamental positive-sequence component, fundamental negative-sequence component, fundamental zero-sequence component, and harmonic components are detected, and a command current is output to the current controller 11 based on the detection results. When the control method is used to control... Figure 3 and Figure 4 When the power quality compensation devices 1c and 1d are shown, the control method further includes the step of: detecting the grid current i using detector 17b. sThe fundamental positive sequence component, fundamental negative sequence component, fundamental zero sequence component and harmonic component are detected, and the command current is output to the current controller 11 based on the detection results.

[0056] In this control method, the controlled power quality compensation device may be, for example, but not limited to, an active power filter, a static var generator, or an enhanced static var generator with harmonic compensation.

[0057] In summary, this disclosure provides a power quality compensation device and its control method. When compensating for harmonics and reactive power generated by nonlinear loads in the power grid, the power quality device predicts the ripple component of the bus voltage based on the voltage and first current at the common connection point between the power grid and the nonlinear load. This prediction is then canceled out with the ripple component of the sampled actual DC bus voltage to obtain the DC component of the DC bus voltage. The power quality compensation device 1a of this disclosure employs a high-bandwidth voltage control loop, improving the response speed of the voltage loop and achieving optimized control of the bus voltage, thereby enhancing the stability of the device and the power quality improvement effect.

[0058] It should be noted that the above are merely preferred embodiments for illustrating this disclosure, and this disclosure is not limited to the described embodiments. The scope of this disclosure is determined by the appended claims. Furthermore, this disclosure may be modified in various ways by those skilled in the art, but all such modifications shall not depart from the protection sought by the appended claims.

Claims

1. A power quality compensation device, electrically connected to a power grid and a nonlinear load, characterized in that, Include: A current controller receives a command current and outputs a switching control signal; A converter, electrically coupled to the current controller, is used to output an output current and an actual DC bus voltage according to the switch control signal; A ripple predictor is used to receive an intermediate voltage and a first current, and output a predicted ripple voltage, wherein the intermediate voltage is the voltage at the common connection point between the power grid and the nonlinear load. A processing unit, electrically connected to the ripple predictor and the converter, is used to obtain the DC component of the actual DC bus voltage based on the actual DC bus voltage and the predicted ripple voltage, and to output a processing result based on the DC component of the actual DC bus voltage and a reference DC bus voltage. as well as A voltage controller, electrically coupled between the processing unit and the current controller, receives the processing result and outputs a voltage control signal to the current controller. Wherein, the first current is the output current, and the ripple predictor outputs the predicted ripple voltage based on the intermediate voltage and the output current. The power quality compensation device further includes a detector electrically connected to the current controller. The detector is used to detect the fundamental positive sequence component, fundamental negative sequence component, fundamental zero sequence component, and harmonic components in the grid current or nonlinear load current, and outputs the command current to the current controller based on the detection results.

2. The power quality compensation device as described in claim 1, characterized in that, The command current is a reference current for the grid current.

3. The power quality compensation device as described in claim 1, characterized in that, The command current is a reference current for the nonlinear load current.

4. A power quality compensation device, electrically connected to a power grid and a nonlinear load, characterized in that, Include: A current controller receives a command current and outputs a switching control signal; A converter, electrically coupled to the current controller, is used to output an output current and an actual DC bus voltage according to the switch control signal; A ripple predictor is used to receive an intermediate voltage and a first current, and output a predicted ripple voltage, wherein the intermediate voltage is the voltage at the common connection point between the power grid and the nonlinear load. A processing unit, electrically connected to the ripple predictor and the converter, is used to obtain the DC component of the actual DC bus voltage based on the actual DC bus voltage and the predicted ripple voltage, and to output a processing result based on the DC component of the actual DC bus voltage and a reference DC bus voltage. as well as A voltage controller, electrically coupled between the processing unit and the current controller, receives the processing result and outputs a voltage control signal to the current controller. Wherein, the first current is the command current, and the ripple predictor outputs the predicted ripple voltage based on the intermediate voltage and the command current. The power quality compensation device further includes a detector electrically connected to the current controller. The detector is used to detect the fundamental positive sequence component, fundamental negative sequence component, fundamental zero sequence component, and harmonic components in the grid current or nonlinear load current, and outputs the command current to the current controller based on the detection results.

5. The power quality compensation device as described in claim 4, characterized in that, The command current is a reference current for the grid current.

6. The power quality compensation device as described in claim 4, characterized in that, The command current is a reference current for the nonlinear load current.

7. The power quality compensation device as described in claim 1 or 4, characterized in that, The power quality compensation device further includes a drive circuit electrically connected between the current controller and the converter, for receiving and outputting a drive signal to the converter according to the switching control signal output by the current controller, and the converter operating according to the drive signal.

8. The power quality compensation device as described in claim 1 or 4, characterized in that, The power quality compensation device is an active power filter, a static var generator, or an enhanced static var generator with harmonic compensation function.

9. A control method applicable to a power quality compensation device, the power quality compensation device being electrically connected to a power grid and a nonlinear load, characterized in that, The control method includes: A current controller is used to receive a command current and output a switching control signal; A converter is used to output an output current and an actual DC bus voltage according to the switch control signal; A ripple predictor is used to output a predicted ripple voltage based on an intermediate voltage and a first current, wherein the intermediate voltage is the voltage at the common connection point between the power grid and the nonlinear load. A processing unit is used to obtain the DC component of the actual DC bus voltage based on the actual DC bus voltage and the predicted ripple voltage, and outputs a processing result based on the DC component of the actual DC bus voltage and a reference DC bus voltage. as well as A voltage controller outputs a voltage control signal to the current controller based on the processing result. Wherein, the first current is the output current, and the ripple predictor outputs the predicted ripple voltage based on the intermediate voltage and the output current. The control method further includes using a detector to detect the fundamental positive-sequence component, fundamental negative-sequence component, fundamental zero-sequence component, and harmonic components of the grid current or nonlinear load current, and outputting the command current to the current controller based on the detection results.

10. The control method as described in claim 9, characterized in that, The command current is a reference current for the grid current.

11. The control method as described in claim 9, characterized in that, The command current is a reference current for the nonlinear load current.

12. A control method applicable to a power quality compensation device, the power quality compensation device being electrically connected to a power grid and a nonlinear load, characterized in that, The control method includes: A current controller is used to receive a command current and output a switching control signal; A converter is used to output an output current and an actual DC bus voltage according to the switch control signal; A ripple predictor is used to output a predicted ripple voltage based on an intermediate voltage and a first current, wherein the intermediate voltage is the voltage at the common connection point between the power grid and the nonlinear load. A processing unit is used to obtain the DC component of the actual DC bus voltage based on the actual DC bus voltage and the predicted ripple voltage, and outputs a processing result based on the DC component of the actual DC bus voltage and a reference DC bus voltage. as well as A voltage controller outputs a voltage control signal to the current controller based on the processing result. Wherein, the first current is the command current, and the ripple predictor outputs the predicted ripple voltage based on the intermediate voltage and the command current. The control method further includes using a detector to detect the fundamental positive-sequence component, fundamental negative-sequence component, fundamental zero-sequence component, and harmonic components of the grid current or nonlinear load current, and outputting the command current to the current controller based on the detection results.

13. The control method as described in claim 12, characterized in that, The command current is a reference current for the grid current.

14. The control method as described in claim 12, characterized in that, The command current is a reference current for the nonlinear load current.

15. The control method as described in claim 9 or 12, characterized in that, The control method further includes using a drive circuit to receive and output a drive signal to the converter based on the switching control signal output by the current controller, wherein the converter operates according to the drive signal.

16. The control method as described in claim 9 or 12, characterized in that, The power quality compensation device is an active power filter, a static var generator, or an enhanced static var generator with harmonic compensation function.

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