Self-adaptive harmonic damping enhancement system and control method thereof

Abstract

The invention discloses a self-adaptive harmonic damping enhancement system and a control method thereof. The system comprises a transformer, the transformer comprises a primary side coil and a secondary side coil, the first end of the primary side coil is connected with a first power supply end, the second end of the primary side coil is connected with the first end of a nonlinear load, and the second end of the nonlinear load is connected with a second power supply end; the first output end of the inverter circuit is connected with the first end of the secondary side coil, and the second end of the inverter circuit is connected with the second end of the secondary side coil; the control module is connected with the control end of the inverter circuit, the control module is used for generating a driving signal output to the inverter circuit according to a preset corresponding relation, and the inverter circuit is used for generating a compensation voltage according to the driving signal and outputting the compensation voltage to the secondary side coil, so that the problem of harmonic oscillation caused by a nonlinear load is solved. The system reliability is improved.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to an adaptive harmonic damping enhancement system and a control method thereof. Background Art

[0002] With the widespread use of power electronic converters, nonlinear loads such as rectifiers, grid-connected power supplies, and switching power supplies are connected to the power grid in large quantities. The resulting harmonic pollution has brought about many power quality problems.

[0003] Therefore, it is particularly urgent to solve the problem of harmonic oscillation generated by nonlinear loads and power electronic equipment. Summary of the invention

[0004] The present invention provides an adaptive harmonic damping enhancement system and a control method thereof, so as to solve the harmonic oscillation problem caused by nonlinear loads and improve system reliability.

[0005] According to one aspect of the present invention, there is provided an adaptive harmonic damping enhancement system, characterized in that it comprises:

[0006] Non-linear loads;

[0007] A transformer, the transformer comprising a primary coil and a secondary coil, a first end of the primary coil being connected to a first power supply end, a second end of the primary coil being connected to a first end of the nonlinear load, and a second end of the nonlinear load being connected to a second power supply end;

[0008] An inverter circuit, wherein a first output end of the inverter circuit is connected to a first end of the secondary coil, and a second end of the inverter circuit is connected to a second end of the secondary coil;

[0009] A control module, the control module is connected to the control end of the inverter circuit, and the control module is used to generate a drive signal output to the inverter circuit according to a preset corresponding relationship; wherein the preset corresponding relationship is a corresponding relationship between a fundamental magnetic flux compensation coefficient and a harmonic magnetic flux compensation coefficient and a duty cycle of the drive signal;

[0010] The inverter circuit is used to generate a compensation voltage according to the drive signal and output it to the secondary coil, wherein the compensation voltage is equal in magnitude and opposite in direction to the harmonic voltage generated by the nonlinear load.

[0011] Optionally, the adaptive harmonic damping enhancement system further includes a damper;

[0012] The damper is connected in parallel to both ends of the secondary coil.

[0013] According to another aspect of the present invention, a control method of an adaptive harmonic damping enhancement system is provided, which is applied to the adaptive harmonic damping enhancement system described above;

[0014] The control method of the adaptive harmonic damping enhancement system includes:

[0015] Acquiring the harmonic voltage of the adaptive harmonic damping enhancement system;

[0016] A drive signal is generated according to the harmonic voltage and a preset corresponding relationship to control the inverter circuit to generate and output a compensation voltage to the secondary side coil; wherein the preset corresponding relationship is the corresponding relationship between the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient and the duty cycle of the drive signal; the compensation voltage is equal to the harmonic voltage in magnitude and opposite in direction.

[0017] Optionally, before generating a driving signal according to the harmonic voltage and a preset corresponding relationship, the method further includes:

[0018] determining a transfer function of an equivalent impedance of a primary side of the transformer;

[0019] Determining an adjustable variable according to a transfer function of an equivalent impedance of a primary side of the transformer; the adjustable variable includes the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient;

[0020] The preset corresponding relationship between the adjustable variable and the duty cycle of the driving signal is established.

[0021] Optionally, determining the transfer function of the equivalent impedance of the primary side of the transformer includes:

[0022] Determining a set of equations of the adaptive harmonic damping enhancement system according to a T-type equivalent circuit of the adaptive harmonic damping enhancement system;

[0023] The transfer function of the equivalent impedance of the primary side of the transformer is determined according to the relationship between the harmonic compensation coefficient, the current on the secondary side of the transformer, the current on the primary side of the transformer, and the equation group of the adaptive harmonic damping enhancement system.

[0024] Optionally, the set of equations of the adaptive harmonic damping enhancement system includes:

[0025] in, is the voltage across the primary coil, Z1 is the leakage impedance of the primary coil, is the current on the primary coil of the transformer, Z m is the excitation impedance of the transformer, Z2 is the leakage impedance of the secondary coil, is the current on the secondary coil of the transformer, is the voltage across the secondary coil;

[0026] The corresponding relationship between the harmonic compensation coefficient, the current on the secondary side of the transformer, and the current on the primary side of the transformer satisfies:

[0027] α is the harmonic compensation coefficient, and the harmonic compensation coefficient is equal to the sum of the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient.

[0028] Optionally, the adaptive harmonic damping enhancement system further includes a damper; the damper is connected in parallel to both ends of the secondary coil;

[0029] According to the relationship between the harmonic compensation coefficient, the current on the secondary side of the transformer, the current on the primary side of the transformer, and the equation group of the adaptive harmonic damping enhancement system, determining the transfer function of the equivalent impedance on the primary side of the transformer includes:

[0030] Determine the conversion transfer function of the equivalent impedance of the primary side of the transformer according to the relationship between the harmonic compensation coefficient, the current on the secondary side of the transformer, the current on the primary side of the transformer, the corresponding relationship between the resistance value of the damper and the fundamental wave extraction function, and the equation group of the adaptive harmonic damping enhancement system;

[0031] determining the excitation impedance of the transformer according to the impedance of the damper;

[0032] The transfer function of the equivalent impedance on the primary side of the transformer is determined according to the conversion transfer function of the equivalent impedance on the primary side of the transformer and the excitation impedance of the transformer.

[0033] Optionally, determining the excitation impedance of the transformer according to the impedance of the damper includes:

[0034] The excitation impedance of the transformer is determined according to the excitation inductance of the transformer and the impedance of the damper.

[0035] Optionally, the impedance of the damper is:

[0036] Among them, Z d is the impedance of the damper, R d is the resistance value of the damper, L d is the inductance value of the damper, C d is the capacitance value of the damper;

[0037] Optionally, the adjustable variable also includes a resistance value of the damper;

[0038] The equivalent impedance transfer function Z of the primary side of the transformereq for:

[0039] Among them, α f is the fundamental flux compensation coefficient, α h is the harmonic system compensation coefficient, L m is the magnetizing inductance, G f is the fundamental wave extraction function.

[0040] The adaptive harmonic damping enhancement system provided by the embodiment of the present invention can adjust the equivalent impedance of the primary side of the system after adjusting the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient. Since the equivalent impedance corresponds to the compensation voltage generated by the system, the magnitude of the compensation harmonics generated by the system can be adjusted by adjusting the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient. The corresponding relationship between the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient and the duty cycle of the driving signal is established in advance, and the adjustment of the magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient is converted into the duty cycle of the adjustment driving signal, so as to adjust the magnitude of the compensation voltage output by the inverter circuit, thereby achieving compensation for the harmonics generated by the nonlinear load in the system.

[0041] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 A schematic diagram of the structure of an adaptive harmonic damping enhancement system provided in Embodiment 1 of the present invention;

[0044] Figure 2 A flow chart of a control method for an adaptive harmonic damping enhancement system provided in Embodiment 2 of the present invention;

[0045] Figure 3 A flowchart of another control method of an adaptive harmonic damping enhancement system provided in Embodiment 2 of the present invention;

[0046] Figure 4 A simplified circuit diagram of an adaptive harmonic damping enhancement system provided in Embodiment 2 of the present invention;

[0047] Figure 5A block diagram of an equivalent admittance model of an adaptive harmonic damping enhancement system provided in the second embodiment of the present invention;

[0048] Figure 6 An adjustable impedance characteristic diagram of an adaptive harmonic damping enhancement system under different harmonic flux compensation coefficients provided in the second embodiment of the present invention;

[0049] Figure 7 A comparison diagram of the amplitude-frequency characteristics of the equivalent admittance of an adaptive harmonic damping enhancement system provided in the second embodiment of the present invention;

[0050] Figure 8 A distribution diagram of the dominant poles of the system under different load power factors in an adaptive harmonic damping enhancement system provided in the second embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0052] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0053] Embodiment 1

[0054] Figure 1 A schematic diagram of the structure of an adaptive harmonic damping enhancement system provided in the first embodiment of the present invention, referring to Figure 1 The system comprises:

[0055] Non-linear load 10;

[0056] The transformer 11 includes a primary coil 111 and a secondary coil 112, wherein a first end of the primary coil 111 is connected to a first power supply terminal A1, a second end of the primary coil 111 is connected to a first end of a nonlinear load 10, and a second end of the nonlinear load 10 is connected to a second power supply terminal A2;

[0057] An inverter circuit 12, wherein a first output terminal of the inverter circuit 12 is connected to a first terminal of a secondary coil 112, and a second terminal of the inverter circuit 12 is connected to a second terminal of the secondary coil 112;

[0058] A control module 13, the control module 13 is connected to the control end of the inverter circuit 12, and the control module 13 is used to generate a drive signal output to the inverter circuit 12 according to a preset corresponding relationship; wherein the preset corresponding relationship is a corresponding relationship between the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient and the duty cycle of the drive signal;

[0059] The inverter circuit 12 is used to generate a compensation voltage according to the driving signal and output it to the secondary coil 112 , wherein the compensation voltage is equal in magnitude and opposite in direction to the harmonic voltage generated by the nonlinear load.

[0060] The nonlinear load includes a first inductor L1, a first capacitor C1 and a nonlinear device 101. The first inductor L1 and the first capacitor C1 are connected in series between the second end of the primary coil 111 of the transformer and the second power supply terminal A2. The nonlinear device 101 is connected between the second end of the primary coil 111 of the transformer and the second power supply terminal A2. The common end connected to the first inductor L1 and the nonlinear device 101 serves as the first end of the nonlinear load 10, and the common end connected to the first capacitor C1 and the nonlinear device 101 serves as the second end of the nonlinear load 10. The nonlinear device 101 includes nonlinear devices such as a rectifier, a grid-connected power supply, and a switching power supply. The transformer 11 and the inverter circuit 12 form an adjustable impedance.

[0061] The first power supply terminal A1 and the second power supply terminal A2 are both power grid output terminals, that is, it can be considered that an AC power source u is connected between the first power supply terminal A1 and the second power supply terminal A2. s The inverter circuit 12 includes a DC power supply u dc and an inverter module 121, wherein a first input terminal of the inverter module 121 is connected to a DC power source u dc The positive terminal of the inverter module 121 is connected to the positive terminal of the inverter module 121, and the second input terminal of the inverter module 121 is connected to the DC power supply u dc The inverter module 121 is used to convert the DC power supply u dc The DC voltage is converted into AC power and output to the secondary coil 112 of the transformer. The inverter module 121 can adopt any inverter circuit in the prior art, and no specific limitation is made to this. Optionally, the inverter module 121 can be a unidirectional inverter circuit.

[0062] The control module 13 stores in advance the correspondence between the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient and the duty cycle of the drive signal. Because after adjusting the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient, the size of the equivalent impedance of the primary side of the system can be adjusted, and since there is a one-to-one correspondence between the equivalent impedance and the compensation voltage generated by the system, the size of the compensation harmonics generated by the system can be adjusted by adjusting the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient. The correspondence between the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient and the duty cycle of the drive signal is established in advance, and the adjustment of the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient is converted into the duty cycle of the drive signal, so as to adjust the size of the compensation voltage output by the inverter circuit 12, thereby realizing compensation for the harmonics generated by the nonlinear load in the system.

[0063] The adaptive harmonic damping enhancement system provided by the embodiment of the present invention can adjust the equivalent impedance of the primary side of the system after adjusting the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient. Since the equivalent impedance corresponds to the compensation voltage generated by the system, the magnitude of the compensation harmonics generated by the system can be adjusted by adjusting the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient. The corresponding relationship between the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient and the duty cycle of the driving signal is established in advance, and the adjustment of the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient is converted into the duty cycle of the driving signal to adjust the magnitude of the compensation voltage output by the inverter circuit, thereby achieving compensation for the harmonics generated by the nonlinear load in the system.

[0064] Continue to refer Figure 1 The primary winding leakage impedance, secondary winding leakage impedance and excitation impedance of the transformer are Z1=sL l , Z2=sL2 and Z m =sL m , where L l is the inductance of the primary winding, L2 is the inductance of the secondary winding, L m is the excitation inductance. According to the T-type equivalent circuit, the circuit equation of the system in the sinusoidal steady state is:

[0065]

[0066] in, is the voltage across the primary coil 111, Z1 is the leakage impedance of the primary coil 111, is the current on the primary coil 111 of the transformer, Z m is the excitation impedance of the transformer 11, Z2 is the leakage impedance of the secondary coil 112, is the current on the secondary coil 112 of the transformer, is the voltage across the secondary coil 112 .

[0067] When the control error can be ignored, the current on the secondary coil can be obtained by multiplying the current on the primary coil and the flux compensation coefficient α, and the expression is:

[0068]

[0069] Substituting formula (2) into the equation in formula (1) yields the equivalent impedance expression of the primary side, as follows:

[0070]

[0071] Continue to refer Figure 1 , Optionally, the adaptive harmonic damping enhancement system further includes a damper 14;

[0072] The damper 14 is connected in parallel to both ends of the secondary coil 112 .

[0073] Optionally, the damper 14 may be an RLC damper, and the impedance Z of the damper is d The expression is:

[0074]

[0075] Among them, R d is the resistance value of the damper 14, L d is the inductance of the damper 14, C d is the capacitance value of the damper 14.

[0076] After the two ends of the secondary coil 112 are connected to the damper 14, the equivalent excitation impedance of the transformer can be expressed as:

[0077]

[0078] According to formula 3 and ignoring the leakage impedance of the primary coil 111, the equivalent impedance of the primary side of the transformer can be expressed as:

[0079] Z eq =(1+α f )(1+α h )Z m (6)

[0080] Where α = α f +α h ; α f is the fundamental flux compensation coefficient, α h is the harmonic flux compensation coefficient.

[0081] Voltage U of the adjustable impedance transformer d and the damping component of the secondary current I d The following relations are satisfied:

[0082] R d I d =G f ·U d (7)

[0083] U d It can be directly measured or calculated based on the primary and secondary currents and the excitation impedance. f Extract the filter transfer function for the fundamental; therefore the damper impedance Z d The expression is:

[0084] Z d =R d / G f (8)

[0085] According to formulas (6) and (7), the transfer function of the primary side equivalent impedance can be finally obtained as:

[0086]

[0087] in,

[0088] From formula (9), we can see that by adjusting α f , α h , R d , the equivalent impedance of the primary side can be adjusted, that is, the size of the compensation voltage generated by the system can be adjusted, and then by determining a suitable set of α f , α h , R d To compensate for the harmonic voltage generated by nonlinear loads. f , α h A corresponding relationship can be established between the duty cycle of the drive signal received by the inverter circuit 12, and the adjustment flux compensation coefficient and the harmonic flux compensation coefficient are converted into the duty cycle of the adjustment drive signal to adjust the magnitude of the compensation voltage output by the inverter circuit. The fundamental flux compensation coefficient and the harmonic flux compensation coefficient jointly determine the duty cycle of the drive signal, R d And the compensation of the inverter circuit output (together constitute the entire equivalent damping to compensate for the harmonics in the power grid.

[0089] Embodiment 2

[0090] Figure 2 This is a flow chart of a control method for an adaptive harmonic damping enhancement system provided in Embodiment 2 of the present invention, with reference to Figure 1 and Figure 2 , the method is executed by a control module, and the method includes:

[0091] S110: Acquire the harmonic voltage of the adaptive harmonic damping enhancement system.

[0092] The presence of nonlinear loads in the system will generate harmonics that affect system stability. A harmonic detector is used to monitor the harmonics of the system to obtain the harmonic voltage of the system.

[0093] S120: Generate a drive signal according to the harmonic voltage and the preset corresponding relationship to control the inverter circuit 12 to generate and output a compensation voltage to the secondary side coil 112; wherein the preset corresponding relationship is the correspondence between the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient and the duty cycle of the drive signal; the compensation voltage is equal to the harmonic voltage in magnitude and opposite in direction.

[0094] Generate the corresponding relationship between the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient and the duty cycle of the drive signal in advance, that is, the fundamental magnetic flux compensation coefficient and the harmonic system compensation coefficient jointly determine the duty cycle of the drive signal. Because after adjusting the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient, the size of the equivalent impedance of the primary side of the system can be adjusted, and since the equivalent impedance corresponds to the compensation voltage generated by the system, the size of the compensation harmonics generated by the system can be adjusted by adjusting the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient. Establish the corresponding relationship between the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient and the duty cycle of the drive signal in advance, convert the adjustment of the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient into the duty cycle of the drive signal, so as to adjust the size of the compensation voltage output by the inverter circuit 12, and then realize the compensation of the harmonics generated by the nonlinear load in the system.

[0095] Figure 3 This is a flowchart of another control method of an adaptive harmonic damping enhancement system provided in the second embodiment of the present invention, referring to Figure 1 and Figure 3 , the method comprising:

[0096] S111: Obtaining harmonic voltage of the adaptive harmonic damping enhancement system.

[0097] S121: Determine a transfer function of the equivalent impedance of the primary side of the transformer.

[0098] The harmonic current introduced by the load is regarded as an independent disturbance factor within the system to distinguish the significant differences in harmonic frequency and value caused by different load types; for the design of the passive power filter, that is, the first inductor L1 and the first capacitor C1 in the nonlinear load 10, considering its negative resistance characteristics mainly exhibited near the fundamental frequency, it is simplified to a capacitor, which mainly undertakes the function of compensating reactive power. In addition, the leakage impedance of the series transformer in the adjustable impedance and the time delay and error that may be introduced by the current measurement and control link are ignored. Since only the resonant characteristics of the system near the fundamental frequency are concerned, in order to further reduce the system order, the nonlinear load 10 can be regarded as a first-order linear impedance, and the system equivalent admittance model block diagram and the mathematical model of the adjustable reactance are obtained. Figure 4 A simplified circuit diagram of an adaptive harmonic damping enhancement system provided in Embodiment 2 of the present invention is shown in FIG. Figure 5 This is a block diagram of an equivalent admittance model of an adaptive harmonic damping enhancement system provided in the second embodiment of the present invention. h is an equivalent current source. h is the voltage across the secondary coil of the transformer, L h is the magnetizing inductance, i s is the current on the primary side of the transformer.

[0099] Optionally, S121 further includes: determining a group of equations of the adaptive harmonic damping enhancement system based on a T-type equivalent circuit of the adaptive harmonic damping enhancement system; determining a transfer function of the equivalent impedance of the primary side of the transformer based on the relationship between the harmonic compensation coefficient, the current on the secondary side of the transformer, the current on the primary side of the transformer, and the group of equations of the adaptive harmonic damping enhancement system.

[0100] Optionally, the adaptive harmonic damping enhancement system also includes a damper; the damper is connected in parallel to both ends of the secondary coil. A damper is added to the secondary side of the adjustable impedance transformer; voltage-current flux compensation is added to the original system, so that the adjustable impedance is equivalent to a certain resistance to the fundamental wave, and the fundamental wave voltage drop of the adjustable impedance is theoretically zero in steady state, so this will not affect the steady-state characteristics of the system. Among them, the transformer and the inverter circuit constitute the flux compensation type adjustable impedance part.

[0101] The leakage impedance of the primary winding (i.e. the primary coil), the leakage impedance of the secondary winding (i.e. the secondary coil) and the excitation impedance of the transformer are Z1=sL l , Z2=sL2 and Z m =sL m According to the T-type equivalent circuit, the circuit equation for the sinusoidal steady state can be obtained as follows:

[0102]

[0103] in, is the voltage across the primary coil 111, Z1 is the leakage impedance of the primary coil 111, is the current on the primary coil 111 of the transformer, Z m is the excitation impedance of the transformer 11, Z2 is the leakage impedance of the secondary coil 112, is the current on the secondary coil 112 of the transformer, is the voltage across the secondary coil 112. l is the inductance of the primary winding, L2 is the inductance of the secondary winding, L m is the magnetizing inductance.

[0104] When the control error can be ignored, the secondary current can be obtained by multiplying the primary current and the flux compensation coefficient α. That is, the relationship between the harmonic compensation coefficient, the secondary current of the transformer, and the primary current of the transformer satisfies:

[0105]

[0106] Among them, the harmonic compensation coefficient is equal to the sum of the fundamental flux compensation coefficient and the harmonic flux compensation coefficient. Substituting formula (11) into formula (10), the expression of the equivalent impedance of the primary side can be obtained as follows:

[0107]

[0108] Since Z1 is relative to Z m is small, therefore, we ignore Z1 and set Z m =jX m Substituting into formula (12), formula (12) can be appropriately simplified as follows:

[0109] Z eq ≈α ⊥ X m +j(1+α)X m (13)

[0110] In the above formula, α=α-jα ⊥ , X m Represents the magnitude of the reactance component of the excitation impedance. Based on the simplified expression, we can understand that by adjusting the flux regulation parameters, the equivalent impedance can be adjusted steplessly in four quadrants in theory. In this process, the real part of the impedance is mainly responsible for adjusting the reactance component, while the imaginary part mainly affects the resistance component.

[0111] In order to achieve independent adjustment of fundamental impedance and harmonic impedance, a filter is needed to separate the fundamental component of the detection current. The fundamental extraction function of the fundamental extraction filter used is:

[0112]

[0113] Usually, the fundamental flux compensation coefficient α is set f =1, so that the fundamental equivalent impedance of the adjustable impedance is close to zero, and the harmonic flux compensation coefficient α is set h ≥0, ignoring measurement and control errors, the equivalent impedance expressions of the generalized flux compensation coefficient and adjustable impedance are as follows:

[0114] α=-G f (s)+α h [1-G f (s)](15)

[0115]

[0116] Where α = α h +G f .

[0117] Figure 6 This is a diagram of adjustable impedance characteristics of an adaptive harmonic damping enhancement system under different harmonic flux compensation coefficients provided in the second embodiment of the present invention. Figure 6 The horizontal axis is the frequency, in Hz, and the vertical axis is the phase (deg) and the harmonic amplitude (dB). Figure 6 The example given in h The amplitude-frequency characteristics are 0, 1, 3 and 5 respectively. It can be seen that near the fundamental wave, the amplitude of the compensation harmonic generated by the system is close to 0, and the adjustable impedance can suppress the harmonic current of the system without affecting the fundamental wave. However, in the frequency band slightly higher than the fundamental frequency, the impedance angle is close to 180°, so there is a non-negligible negative resistance component, which can generate compensation harmonics to offset the harmonics generated by the nonlinear load.

[0118] The mathematical model of the adjustable reactance can be obtained by selecting the parameters other than time and frequency to be normalized, selecting the system rated voltage and the load rated active power as the reference values, and setting the power factor to λ, and using the following equation to obtain: Figure 4 Medium impedance Z load expression.

[0119]

[0120] Can be obtained:

[0121]

[0122] in, X load =ω f ·L load .

[0123] Further, according to the relationship between the harmonic compensation coefficient, the current on the secondary side of the transformer, the current on the primary side of the transformer, and the equation group of the adaptive harmonic damping enhancement system, the transfer function of the equivalent impedance on the primary side of the transformer is determined to include:

[0124] According to the relationship between the harmonic compensation coefficient, the current on the secondary side of the transformer, the current on the primary side of the transformer, the relationship between the resistance value of the damper and the fundamental wave extraction function, and the equation group of the adaptive harmonic damping enhancement system, the conversion transfer function of the equivalent impedance on the primary side of the transformer is determined; the excitation impedance of the transformer is determined according to the impedance of the damper; the transfer function of the equivalent impedance on the primary side of the transformer is determined according to the conversion transfer function of the equivalent impedance on the primary side of the transformer and the excitation impedance of the transformer.

[0125] Specifically, the conversion transfer function of the equivalent impedance of the primary side of the transformer is the expression shown in (12). Determining the excitation impedance of the transformer according to the impedance of the damper includes: determining the excitation impedance of the transformer according to the excitation inductance of the transformer and the impedance of the damper. Specifically, when an RLC damper is used, the expression of the impedance of the damper is:

[0126]

[0127] R d is the resistance value of the damper 14, L d is the inductance of the damper 14, C d is the capacitance value of the damper 14, Z d is the impedance of the damper.

[0128] After the two ends of the secondary coil 112 are connected to the damper 14, the equivalent excitation impedance of the transformer can be expressed as:

[0129]

[0130] According to formula (12) and after ignoring the leakage impedance of the primary coil 111, the equivalent impedance of the primary side of the transformer can be approximately expressed as:

[0131] Z eq =(1+α f )(1+α h )Z m (twenty one)

[0132] Voltage U of the adjustable impedance transformer d and the damping component of the secondary current I d The following relations are satisfied:

[0133] R d I d =G f ·Ud (twenty two)

[0134] In the formula, U d It can be directly measured or calculated based on the primary and secondary currents and the excitation impedance. f is the fundamental extraction function of the fundamental extraction filter; therefore, the impedance Z of the damper d The expression is:

[0135] Z d =R d / G f (twenty three)

[0136] Finally, the transfer function of the equivalent impedance of the primary side of the transformer is Z eq for:

[0137] Among them, α f is the fundamental flux compensation coefficient, α h is the harmonic system compensation coefficient, L m is the magnetizing inductance, G f is the fundamental wave extraction function.

[0138] The amplitude-frequency characteristics of the system equivalent admittance after adding the damper can be found in Figure 7 , Figure 7 A comparison diagram of the amplitude-frequency characteristics of the equivalent admittance of an adaptive harmonic damping enhancement system provided in the second embodiment of the present invention, Figure 7 The horizontal axis is the frequency, in Hz, and the vertical axis is the phase (deg) and the harmonic amplitude (dB). Figure 7 R is given as an example d 0, 10 respectively 6 , 0.7 amplitude-frequency characteristic diagram. It can be seen that by adjusting R d The size can be used to adjust the harmonic amplitude.

[0139] For the distribution diagram of the dominant pole of the system under different load power factors, see Figure 8 As shown, Figure 8 A distribution diagram of the dominant poles of the system under different load power factors in an adaptive harmonic damping enhancement system provided in the second embodiment of the present invention, Figure 8 The horizontal axis is the real part, and the vertical axis is the imaginary part. Figure 8 The blue part in the middle represents the capacitive load, and the red part represents the inductive load. Compared with the original system, after adding the damper, the system poles are turned to the left half plane around the fixed point corresponding to the fundamental frequency on the imaginary axis. Regardless of whether the load is inductive or capacitive, as long as |λ is not too small, the system will have good stability and transient characteristics.

[0140] S131: Determine adjustable variables according to the transfer function of the equivalent impedance of the primary side of the transformer; the adjustable variables include a fundamental magnetic flux compensation coefficient and a harmonic magnetic flux compensation coefficient.

[0141] After adding the damper, the adjustable variable also includes the resistance of the damper. By adjusting the fundamental magnetic flux compensation coefficient, the harmonic magnetic flux compensation coefficient and the resistance of the damper, the equivalent impedance of the primary side of the transformer can be adjusted, thereby achieving the adjustment of the compensation harmonics.

[0142] S141: Establishing a preset corresponding relationship between the adjustable variable and the duty cycle of the driving signal.

[0143] The fundamental wave magnetic flux compensation coefficient and the harmonic wave magnetic flux compensation coefficient jointly determine the duty cycle of the drive signal, and the duty cycle of the drive signal determines the magnitude of the compensation voltage output by the inverter circuit.

[0144] S151 : generating a driving signal according to the harmonic voltage and a preset corresponding relationship to control the inverter circuit 12 to generate and output a compensation voltage to the secondary side coil 112 .

[0145] The fundamental wave magnetic flux compensation coefficient and the harmonic wave magnetic flux compensation coefficient are converted into the duty cycle of the adjustment driving signal to adjust the magnitude of the compensation voltage output by the inverter circuit 12, thereby compensating for the harmonics generated by the nonlinear load in the system.

[0146] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0147] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An adaptive harmonic damping enhancement system, characterized in that: include: Non-linear loads; A transformer, the transformer comprising a primary coil and a secondary coil, a first end of the primary coil being connected to a first power supply end, a second end of the primary coil being connected to a first end of the nonlinear load, and a second end of the nonlinear load being connected to a second power supply end; An inverter circuit, wherein a first output end of the inverter circuit is connected to a first end of the secondary coil, and a second end of the inverter circuit is connected to a second end of the secondary coil; A control module, the control module is connected to the control end of the inverter circuit, and the control module is used to generate a drive signal output to the inverter circuit according to a preset corresponding relationship; wherein the preset corresponding relationship is a corresponding relationship between a fundamental magnetic flux compensation coefficient and a harmonic magnetic flux compensation coefficient and a duty cycle of the drive signal; The inverter circuit is used to generate a compensation voltage according to the drive signal and output it to the secondary coil, wherein the compensation voltage is equal in magnitude and opposite in direction to the harmonic voltage generated by the nonlinear load.

2. The adaptive harmonic damping enhancement system according to claim 1, characterized in that: Also included are dampers; The damper is connected in parallel to both ends of the secondary coil.

3. A control method for an adaptive harmonic damping enhancement system, characterized in that: Applicable to the adaptive harmonic damping enhancement system as claimed in claim 1 or 2; The control method of the adaptive harmonic damping enhancement system includes: Acquiring the harmonic voltage of the adaptive harmonic damping enhancement system; A drive signal is generated according to the harmonic voltage and a preset corresponding relationship to control the inverter circuit to generate and output a compensation voltage to the secondary side coil; wherein the preset corresponding relationship is the corresponding relationship between the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient and the duty cycle of the drive signal; the compensation voltage is equal to the harmonic voltage in magnitude and opposite in direction.

4. The control method of the adaptive harmonic damping enhancement system according to claim 3, characterized in that: Before generating a driving signal according to the harmonic voltage and the preset corresponding relationship, the method further includes: determining a transfer function of an equivalent impedance of a primary side of the transformer; Determining an adjustable variable according to a transfer function of an equivalent impedance of a primary side of the transformer; the adjustable variable includes the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient; The preset corresponding relationship between the adjustable variable and the duty cycle of the driving signal is established.

5. The control method of the adaptive harmonic damping enhancement system according to claim 4, characterized in that: The transfer function for determining the equivalent impedance of the primary side of the transformer includes: Determining a set of equations of the adaptive harmonic damping enhancement system according to a T-type equivalent circuit of the adaptive harmonic damping enhancement system; The transfer function of the equivalent impedance of the primary side of the transformer is determined according to the relationship between the harmonic compensation coefficient, the current on the secondary side of the transformer, the current on the primary side of the transformer, and the equation group of the adaptive harmonic damping enhancement system.

6. The control method of the adaptive harmonic damping enhancement system according to claim 5, characterized in that: The set of equations of the adaptive harmonic damping enhancement system includes: in, is the voltage across the primary coil, Z1 is the leakage impedance of the primary coil, is the current on the primary coil of the transformer, Z m is the excitation impedance of the transformer, Z2 is the leakage impedance of the secondary coil, is the current on the secondary coil of the transformer, is the voltage across the secondary coil; The relationship between the harmonic compensation coefficient, the current on the secondary side of the transformer, and the current on the primary side of the transformer satisfies: α is the harmonic compensation coefficient, and the harmonic compensation coefficient is equal to the sum of the fundamental magnetic flux compensation coefficient and the harmonic magnetic flux compensation coefficient.

7. The control method of the adaptive harmonic damping enhancement system according to claim 6, characterized in that: The adaptive harmonic damping enhancement system further comprises a damper; the damper is connected in parallel to both ends of the secondary coil; According to the relationship between the harmonic compensation coefficient, the current on the secondary side of the transformer, the current on the primary side of the transformer, and the equation group of the adaptive harmonic damping enhancement system, determining the transfer function of the equivalent impedance on the primary side of the transformer includes: Determine a conversion transfer function of an equivalent impedance on the primary side of the transformer according to a harmonic compensation coefficient, a current on the secondary side of the transformer, a relationship between a current on the primary side of the transformer, a relationship between a resistance value of the damper and a fundamental wave extraction function, and an equation group of the adaptive harmonic damping enhancement system; determining the excitation impedance of the transformer according to the impedance of the damper; The transfer function of the equivalent impedance on the primary side of the transformer is determined according to the conversion transfer function of the equivalent impedance on the primary side of the transformer and the excitation impedance of the transformer.

8. The control method of the adaptive harmonic damping enhancement system according to claim 7, characterized in that: Determining the excitation impedance of the transformer according to the impedance of the damper includes: The excitation impedance of the transformer is determined according to the excitation inductance of the transformer and the impedance of the damper.

9. The control method of the adaptive harmonic damping enhancement system according to claim 8, characterized in that: The impedance of the damper is: Among them, Z d is the impedance of the damper, R d is the resistance value of the damper, L d is the inductance value of the damper, C d is the capacitance value of the damper.

10. The control method of the adaptive harmonic damping enhancement system according to claim 9, characterized in that: The adjustable variable also includes the resistance value of the damper; The equivalent impedance transfer function Z of the primary side of the transformer eq for: Among them, α f is the fundamental flux compensation coefficient, α h is the harmonic system compensation coefficient, L m is the magnetizing inductance, G f is the fundamental wave extraction function.

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