TW548886B - Three-phase shunt type active power filter capable of operating in parallel - Google Patents

Abstract

Compared with other types of active power filters, the shunt type active power filter requires to process a larger portion of load power. Therefore, if the filter is implemented by high frequency switching type switches, the capacity of the filter is limited by the voltage and current capable of being reached by the switches. To overcome such a problem, the present invention provides a control method capable of limiting the output capacity of the active power filter, and a method for sensing the serial load current, so that the filter is formed by multiple sets connected in parallel without having a control signal connection, thereby increasing the system capacity and increase the reliability. The inventive filter is suitable for three-phase three-wire and three-phase four-wire systems, and can compensate the virtual power of the load, and non-balance of harmonic current and three-phase current, thereby making the input current to be a low-distorted waveform having a phase same as the voltage, and the current of neutral line (three-phase four-wire system) to be zero. In addition, the present invention also provides: (1) a PWM switching method of three-phase four-wire converter to decouple the switching of the switch of each arm to reduce the complexity of the controller; (2) a circuit architecture using a small capacitor serially connected to the neutral line of the input power so as to remove the high-frequency switching current harmonic waves on the neutral line thereby preventing conductive EMI.

Description

Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs 548886 V. Description of the invention ([new technology field] Electric furnace = operation: two; two phases: parallel operation of parallel active current, unbalanced power supply, etc. — Type of filter. Material load virtual work, spectral wave [prior technology] In recent years, the conversion of semiconductor power components has been more diverse, flexible and flexible. ^ Energy, body rectifiers, gate fluid converters and :: : Big! "Two-phase system (UPS) and other pre-level rectifiers, dwellers, and continuous electricity, have also caused the power transmission and distribution system phase? The use of the skin 丨 serious tanks, effective power , Voltage surges, electromagnetic interference and common ..., the problem of surface recognition. Traditional passive filters are based on the power industry to remove specific harmonics, although it is simple and cheap, and the performance of each filter is deeply affected by the load than private perception. Characteristic impact, such as lack of white vibration and…, 6. The active Greek filter uses power converters for power vision 7 < conversion and adjustment to simultaneously improve current harmonics and compensate for virtual failure.

Moreover, the problem of A filter characteristic deviation is in the foreseeable and passive filters. Active power filtering is not a good idea * V 丄 久 咨 取 often used as a shunt structure. Its advantage is to provide harmonic current, virtual dagger force and even current Unbalanced, the disadvantage is that the converter needs to deal with relatively large power, so: if the switching element such as BJT and IGBT is used to implement the converter, the capacity of the filter will be reached by the switch :: limited . $ And this paper size is applicable to China National Standard (CNS) A4 specification (210X297mm) ........... f ——...:, Yiding :: ......... Φ (Please read first Note on the back, please fill out this page again; 548886 Α7 Β7 V. Description of the Invention () The most commonly used method of the control technology of the parallel active power filter is the Instantaneous-re active-power algorithm. algorithm) and Synchronous-detection algorithm. The instantaneous virtual power algorithm is based on the axis conversion and converts the voltage and current from the three-phase abc axis to the dq coordinate axis:

a 6.C .............. (Please read the note Ϋ-item on the back before filling in this page) 91 The real-time instant load of the power deficiency and PI power is given by (1), (2) The formula can be calculated ^ PL, d eq {Ld JL_ re < i ed_ 'pl ^ pl] where the AC component uses the word load power as the filter user / change to get the required complement. 4 The formula is shown: ¥ 波Caused by the power, the negative f command to be compensated for the power command to be compensated is reversed by the current command signal of the lean, such as (4) and (5). eq • 氺} 〇q- ed * · * loa 1 0 i〇b = -1 2 λ / 3 2 loc -1 —V3 LJ ST 2 J lod

-1 ^ PL (4) (5) If you want to work, only modify the heart in (4) to heart + t is 5

"Η \ zl ζί β (1 eq 2 2 〇 f -Lu • eb L» J "L 2 2 J kd

V I zl ιύ. 2 2 〇 Inter This paper size applies the Chinese National Standard (CNS) A4 specification (210X 297) 548886 A7 B7 V. Description of the invention () Yes. The advantage of this algorithm is that it is suitable for three-phase voltage imbalance, but the disadvantage is that it needs to sense the voltage and current and does not have the function of compensating the load current imbalance. The synchronous detection algorithm assumes that the three-phase voltage is balanced and distortion-free. The three-phase instantaneous power is: P = iea eb ecl · (6) After the low-pass filter, the DC value of the sum of the three-phase load power can be obtained, so the actual power of the individual input of the three-phase power can be obtained by the following formula. : = F · X— Pb Eb Λ. ⑺ where ', & and Wu are the amplitudes of the three-phase voltages, and five are the sum of the amplitudes of the three-phase voltages. In this way, the basic wave current command of the three-phase input current can be obtained: * lsa · * hb. * Lsc leaPa / 2ebPby ............. MW —— 、： …… ， 可. ........ φ urn-^ * (Please read the notes on the back before filling this page) Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs ^ eC ^ Cy

Ea k (8) The current command signal of the filter can be obtained by subtracting the load current:

· Ζ I _ ^ _ I ha a iLa *. Hb ~ ^ Lb • 氺. He ~ ^ Lc (9) This algorithm is very simple and can also compensate for the three-phase negative. 6 The paper size applies the Chinese National Standard (CNS) A4 specification (210X297 mm) 548886 Printed by A7 B7, Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs 5. Description of the invention () Unbalanced load function, but when the input voltage is unbalanced or the distortion is severe, its operating performance will be greatly affected . In terms of increasing the capacity that the filter can handle, the conventional methods are multiple sets of different frequency current methods and multiple sets of different switching frequency methods. The method of multi-group compensation for different frequency currents is shown in the 50Hz system of Figure 1. The synchronous detection algorithm is used to estimate the current signal to be compensated, and then it is decomposed into compensation signals of different frequency ranges. The current component in the frequency range is compensated. This method is obvious because each group of converters has its specific frequency compensation range, so when one group of converters fails, it will damage the result of the compensation current of the entire system, so the reliability is also low. The method of multiple sets of different switching frequencies is shown in Figure 2. Multiple sets of active power filters with different switching frequencies are connected in parallel between the power supply and the load. Harmonic magnitude is inversely proportional to the harmonic order and the virtual work current component is low frequency. Use a GTO filter with large capacity but low switching frequency near the load to compensate for virtual work and lower frequency harmonics; The remaining uncompensated higher order harmonics are compensated by IGBT filters near the power supply side with higher switching frequency. This method uses the instantaneous virtual power algorithm to calculate the compensation command current, which has a very good effect on the compensation of various levels of harmonics, and there is no need for a control signal connection between the filters. However, its disadvantage is that when the large-capacity GTO filter is damaged or faulted, the remaining small-capacity filter cannot support a large amount of load harmonic current, so the reliability needs to be strengthened. This paper size is applicable to China National Standard (CNS) A4 specification (210X 297 mm) ......... MW ——- Order ......... **-· · * · (Please read the precautions on the back before filling this page) 548886 V. Description of the invention ([Contents of the invention] (Please read the precautions on the back before filling out this page) Point, the second active power filter control of the present invention Each device control of the method ^ & Filter power, batch / characteristics that replace current compensation with current compensation. (1) At the same time, it has the function of shoulder load measurement: wave: current and three-phase current imbalance; (2) ) No need for ^ conditions; i: only need to detect the voltage phase angle, for the operating performance of the voltage distortion device; (3) can individually limit the amount of work, spectral current and three-phase unbalanced current If the dissolved part of the self-loading unit is insufficient, it can also operate normally. Including "(4) Except for the direct voltage adjustment," each component is self- = reading: compensation of current and three-phase current imbalance. The line "system" has a very high stability; it is suitable for a three-phase three-two-two-mesh four-wire system. The present invention also proposes a three-phase ... The cut-off of the arm switch I is decomposed to reduce the complexity of the controller, and a method of switching the current harmonics of the neutral line frequency is proposed χ " to prevent conductive electromagnetic interference. Based on this, there are limitations Content; Biegu set the power filter, printed by the Consumers' Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs, and also produced multiple sets of filters, which can be connected directly and in parallel to expand the system. None ( The characteristics of the valley are: 不同 The difference from the previous parallel method is that the if-link filters use the same-control method, the parallel system is the earliest, and has the flexibility of different filter capacity; ⑺ uses series connection (load current sensing Mode, so that each filter does not need a control signal connection to automatically achieve the function of shunting; (3) The concept of N + 1 疋 redundancy can be applied, so both the reliability and the 8 paper sizes are applicable to China Standard (CNS) A4 specification (210X297 mm) 548886 A7 B7 5. Description of the invention () The flexibility of parallel connection is higher than other methods. [Embodiment] (Please read the precautions on the back before filling this page) The present invention The method, characteristics and function effect are explained in more detail according to the embodiment of the accompanying drawings. As shown in FIG. 3, the circuit structure of the active power filter proposed by the present invention is shown, and the power filter (F) is connected to the power source in parallel. Between the load and the load (1), it is used to compensate the load's current harmonics, virtual work, and imbalance, so that the three-phase input current is balanced, low distortion, and in phase with the voltage to achieve the power factor of one. It can be commonly used in Three-phase three-wire system or three-phase four-wire system: (1) When applied to a three-phase four-wire system, the filter converter (2) has four switching arms (A, B, C and N arms), where the N arm is connected to the neutral line of the power supply, the purpose of which is to compensate the zero sequence current of the load so that the neutral current of the input current is zero. When the filter works normally, the load neutral is connected to the power neutral through the capacitor CV, so that the power neutral can attenuate the high-frequency switching current harmonics; when the filter stops, the TRIAC switch is turned on Bypass CV so that the zero sequence current of the load can flow. Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs (2) When applied to a three-phase three-wire system, the N arm can be removed. Other functions and control methods are the same as the three-phase four-wire system. The filter converter is switched using a pulse width modulation (PWM) circuit (3) to perform pulse width modulation switching. The control of the filter system is double loop, the inner loop is a current control circuit (inner loop current controller) (4), and the outer loop is harmonic current compensation, virtual 9 This paper size applies to China National Standard (CNS) A4 specifications ( 210X297 mm) 548886 A7 B7 V. Description of the invention () Power compensation, unbalanced current compensation, and DC voltage adjustment circuits (outer loop controller) (5). The outer loop circuit calculates the current commands (44 and 4) that the filter needs to compensate based on the load current. The purpose of the inner loop current controller is to make the filter output current (/ ^, and "c) follow the current commands closely. The following details the principle and operation of each part: 1. The switching control of the converter can be obtained from the circuit in Figure 3: L ^ = Vao-Vsa-VNo (10) at L ^ -Vb0-Vsb-VNo (11) at L ^ t = Vc. -Vsc-Vn〇 (12) Under PWM switching, the output voltage of each switching arm ignoring high frequency switching terms can be expressed as:

Vi〇- ^ V ^) Vd, i = b, c9 N (13) 2 2vtm where • is the control voltage of each arm PWM, v⑺ is the amplitude of the PWM triangle wave, and 6 is the voltage on the DC side of the converter. (10) + (1 1) + (12) and substituting (13) for: L ^ ~ = ^ pwmvconN (^ sa ^ sb ^ sc) ~ ^ pwm (vcona vconb + vconc) (1 4) where Converter voltage gain. Let the control voltage of the N arm be: ............. install! * *-(Please read the notes on the back before filling out this page), \ 一 泛 Φ Printed by the Consumer Consumption Cooperative of Intellectual Property Bureau of the Ministry of Economic Affairs 10 548886 A7 B7 V. Description of Invention (

vcortN \ vsa ^ vsb + vsc) 3k (15) pwm Then (10), (11), (12) and (14) can be expressed as:

L

dL oa kpwmvcona (2Vsa—Vsb—Vsc) (16)

τ dI〇b _ u v (^ Vsa + 2Vsb ^ Vsc) L · —— — ^ pwmvconb I (17)

LdI〇c dt k pwmvconc (-Vsa-Vsb ^ 2Vsc) (18) (Please read the precautions on the back before filling this page)

L

dIoN '^ pwm (vcona + vconb + vconc) (19) Printed by (16), (17), and (18) of the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs, as long as the control voltage of the N arm is set as shown in (15), The control of L6 and is only related to the control voltage of its related arm, and is not affected by the control voltage of other arms. The current of the N arm has nothing to do with its control voltage. Its waveform is determined by the sum of / ~, /, and these. These characteristics can be used to simplify the complexity of the controller design. Equations (16) to (18) will be used as the circuit model of the converter to design the controller of the current loop. 2. Current loop controller The block diagram drawn according to formulas (16) to (18) and the designed current controller are shown in Figure 4, where h and h are the sensing coefficients of voltage and current, respectively. There is a separate controller for each phase current. The control component of each controller is divided into two parts. One is the forward control part (V ///, ζ · = β, & or C), and the other is the feedback control part. (V / 5 /, ζ · = α, 厶, or C). The forward control part is used to offset the voltage of each phase and the current is back to 11. The paper size is applicable to the Chinese National Standard (CNS) A4 specification (210 × 297 mm) 548886. Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs A7 B7 5. Invention Explanation () The disturbance of the circuit; The gain of the error amplifier of the feedback control is ^ /. Once the disturbance of the phase voltage can be eliminated by the forward control part, the response speed of the current loop is determined by A: /: hi __ w ^ pwm ^ s ^ I (1 C \\ W can be regarded as the bandwidth of the current loop. 3. Block diagram of the external loop controller The external loop controller is shown in Figure 5, which is used to generate the above current controller commands. To simplify the control The circuit and external loop controller are designed to execute the circuit parameters from the abc axis to the dqO axis. The relationship between the abc axis and the dq axis is shown in Figure 6. First, the sensed load current is passed through the abc-dqO The conversion circuit is turned to the dqO axis. Since the obtained zero-sequence current needs to be compensated by the Nth arm of the converter so that the neutral current of the input current is zero, the zero-sequence current command of the converter is set to / 〖〇 = / μ .External loop controller includes: 1) Harmonic current compensator (52), unbalanced current compensator (5 3), voltage regulator (54), etc., and each controller circuit is divided into d, q two axis components, and finally d, q two The axis current command is obtained by adding up the current commands calculated by these controller circuits separately. The following explains the principle of each control circuit separately: Virtual work compensator The virtual work compensator is used to calculate the current component required to compensate the virtual power of the load. Since the load compensation of the present invention is current-oriented, the potential imbalance and distortion of the voltage are ignored, and the paper size of this paper applies the Chinese National Standard (CNS) A4 specification (210 X 297 mm) ... ......... 0 ^ —————— Order --------- Φ * *-r < · (Please read the notes on the back before filling this page) 548886 A7 B7 V. Explanation of the invention The synchronous reference signal is used to replace the actual voltage in the () control circuit. First calculate the instantaneous virtual power by the following formula: W Ψ q = = vyd-vdiq = id cos A-iq sin A (2 1) (Please (Please read the notes on the back before filling this page) The first item of the above formula can be regarded as the virtual power of the d-axis, and the second item is q-axis virtual power 'sinA and cosd are reference signals in phase with the d-axis and q-axis, respectively (please refer to Figure 6). Then use a low-pass filter (L p F) to extract the average power component of the instantaneous virtual power' and Limit the capacity of the virtual work to be compensated by the limiter. Finally, multiply it by a proportional factor and the relative reference signal to get the d and q axis's virtual work compensation current commands 'and'. Turbidity current compensator q Ming harmonic current compensation The device is used to calculate the current components required to compensate the harmonic current of the load. It first uses a band-pass filter (BPF) (5 2 1) to find the basic wave components of the d and q two-axis load current ^ and b, i ′ Then subtract the original signal from the basic wave component to get the distortion component of the load current. You and the heart, and finally pass the limiter (522) to limit the distortion current amplitude to obtain the current harmonic components needed to be compensated. Also, iq , Dis. Unbalanced current compensator Printed by the Consumer Property Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs, a two-phase current balance system, whose currents d and q are also balanced. The method of this compensator is to redistribute the power so that the inputs of the two axes d and q The power is equal. Since the virtual power part has been compensated by the virtual power compensator, the compensation of the unbalanced current only needs to consider the real power part here. With the description of the virtual power compensator, the instantaneous real power of the proposed system can be calculated as follows: P = v (dq) * \ dq) = vdld + vqiq = ld sin A + lq cos A (22) 13 This paper is applicable to China National Standard (CNS) A4 specification (210 X 297 mm) 548886 A7 B7 V. Description of the invention () (Please read the precautions on the back before filling this page) The second item in the above formula can be regarded as the real power of the d-axis. The two terms are the real power of the q axis. The load current is calculated by the above formula and the low-pass filter (LPF) (53 1) can be used to obtain the average real power and P-cut of the load on the d-axis and q-axis, respectively. The average value of the two is the current balance when When d, q two axes must input the real power. Therefore, the average value; the difference Aρμ and AP cut from Pω and Θ cut are the real power that the filter needs to compensate on the d and q axes respectively. After the difference between the two real powers passes through the limiter (532) to limit its compensation capacity, it is finally multiplied by a proportional factor h and the relative reference signal to obtain the current command required to balance the d and q two-axis input currents. Voltage regulator Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs Due to the loss of the converter circuit, the converter itself must also absorb real work to compensate for the loss, so that the capacitor voltage on the DC side can be maintained. The voltage regulator feedbacks the DC voltage and compares it with the voltage set value (4). The error is adjusted by the voltage controller (Gv) (541) and multiplied by the reference signal in phase with the voltage to obtain the current command required to maintain the DC voltage. . Since this command and the above unbalanced current compensator are both real work current commands, in practice, the two are actually added and then multiplied by the reference signal to obtain the filter's real work current commands 'and 4' as shown in the figure. 5 shown. The voltage controller Gv can be any type of compensator, and the most commonly used is proportional integral control. The current command components obtained by the above control circuits are added to obtain the current commands 0 and 'of the d-axis and the q-axis. Together with the current command of the 0-axis, the current command for conversion on the abc axis is obtained through the dqO-abc axis conversion circuit ^ , &Amp; and. This paper size applies the Chinese National Standard (CNS) A4 specification (210X297 mm) 548886 A7 B7 V. Description of the invention () (Please read the precautions on the back before filling this page) Figure 7 shows the application of the invention to three-phase Four-wire operation example waveforms, among which the three-phase load current αh c) is inductive, the distortion is severe and unbalanced (as can be seen from the load neutral line current / zv), and the input current (/ ^, / ^, /, C) are balanced, low distortion and in phase with the input voltage (, Fd, 6C), and the current of the load neutral line is fully compensated by the Nth arm of the converter, so the current of the input neutral line (/, #) Is zero. It is worth noting that through the design of the capacitor CV of the present invention, most of the high-frequency ripple current switched by the converter is circulated between the load and the converter, so the current input to the neutral line has almost no high-frequency ripple current component. . The principle is shown in the equivalent circuit at the high-frequency switching frequency of 10, as long as the value of the capacitor 6V is far lower than the value of the two filter capacitors 6V connected in parallel, the south frequency harmonic current (/. ^) Will be Most of the C / flowing through the three parallel connections make the high-frequency harmonic current (/ sD) of the neutral line of the power supply nearly zero. However, if no capacitor is added, it will completely flow through the power supply neutral. 4. Parallel connection of filters Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs, the parallel method of the filter (F) mentioned in the present invention is shown in Figure 8. The filters are connected in parallel between the power supply and the load. Sensing is cascaded, which is characterized in that each filter regards all filters on its load side as part of its load, and its sensed load current is compensated by all filters on its load side What remains afterwards, so as long as the capacity of the filter compensation is limited, the parallel system can allow the filters that actually participate in the parallel to shunt naturally. For example, if a 90KVAR load is borrowed from 15 paper sizes to apply the Chinese National Standard (CNS) A4 specification (210X 297 mm) 548886 A7 V. Description of the invention () A plurality of 20KVAR filters are connected in parallel to compensate to Figure 8 (No. 1 formula will have 20KVAR for No. 1 ~ 4 filters, and 0KVAR for No. 5 filters, so No. (Please read the precautions on the back before filling this page) 1 ~ 4 The main output filters will be evenly shunted. In addition to the high reliability of the parallel connection method that does not require control signal connections between the filters, the system stability is quite high, even when the load capacity exceeds the capacity of all parallel filters , The system can also work normally under the condition of compensating part of the load current or virtual work. Because of this, the system's fault tolerance ability is quite high, even if there is a module failure, it does not hinder the normal operation of the system. It can also be online (〇 n_Hne) under the condition of disassembling and filtering for maintenance without power off, so the flexibility of parallel connection is quite large. The above description of limiting the capacity of the filter is only a brief indication. The filter has functions of compensating the load's virtual power, harmonic current, and three-phase current imbalance. Therefore, the actual capacity limitation method includes the limitation of the above three components. The amount printed by the employee's consumer cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs Limit (2m), distortion current amplitude limit (/ magic and three-phase current unbalanced real power limit (for example, if there are 5 filters connected in parallel as shown in Figure 8, its capacity limit is :, / m = 1〇A, ~ = 1KW, when the load is provided—virtual work i6 5kvar, distortion current 25A, and three-phase current unbalanced maximum two-phase real power difference L7KW, the proposed parallel system is under the above three components. The shunting method is shown in Figure 8 (a), Figure 8 (b), and Figure 8 (c). There will be four filters (editors) to participate in the virtual work compensation, and the three paper sizes are applicable to China. Standard (CNS) A4 size (210X297 mm) 548886 A7

V. Description of the invention () == "3) Participation in spectral wave current compensation, two filters Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs :) Participation in two-phase load current imbalance compensation. The detailed description is as follows: Virtual work compensation As shown in Figure 8 (a), the virtual work generated by the load is 3.30. The result of the first set of filtering benefits calculated through tilt measurement is that the load virtual work is ㊈ ㈣ = 3 ·) is greater than the limit value ⑸, so the " and filter :: If you supply ⑹ to the power system, the input current: the power is 2.3 ⑹. The virtual work βί2 in the load current calculated by the second set of filters is equal to 2 3 n a- 1 »Two, ·, "" The virtual power provided by the two sets of filters, such as the input power of the power system, is 端 1.3 胄. Similarly, after the compensation of the third group of the wave filter, the virtual work of the fourth group to compensate for b is only G3 ~, and after the compensation of the fourth group of filters, the load current measured by the subsequent filter is Without the component of virtual work, the power end does not need to provide virtual work to the load to achieve a power factor of one. Harmonic current capture $ # The load distortion current generated by the load is ~ ㈣ ~, the first / group of filters. The load distortion current calculated through detection is & ice (h this = 仏 this = 2.5½) is greater than the limit value ~, So the i-th filtering benefit only provides the distortion current with the amplitude as the heart to the power system, so that the distortion current amplitude of the input current of the filter 1 is 15 cores. The distortion current amplitude of the load current calculated by the second group of filters is & and is equal to 1 · 5, and the distortion current provided by the second group of filters is ~ 17. Please read the back · I i 4 items and then-I The size of the bound paper is applicable to the Chinese National Standard (CNS) A4 specification (210X 297 mm) 548886 A7 B7_ V. Description of the invention () (Please read the precautions on the back before filling this page) The current amplitude at the input end of the power system The distortion current amplitude is 0 · 5 / slave. Similarly, '43 of the third group of filters, and = 0.5 / μ 'After compensation by the third group of filters, the load current detected by the subsequent filters has no harmonic components, so in the end There is no return of harmonic current at the power end, which affects the power quality. Three-phase unbalanced current compensation Figure 8 (c) The unbalanced real power generated by the load is Δ & = 1.7%. The unbalanced real power of the load detected by the first group of filters is = 1.7PM, which is greater than the limit value. Therefore, the first group of filters only provides% unbalanced real work to the power system, so that the magnitude of the unbalanced real work in the input current is 0.7. The load unbalanced real work detected by the second group of filters is ΔPl 2 = 0 · 7 / M, and the filter 2 only provides 0.7 unbalanced real work to the power system. After being compensated by filter 2, the power system current will no longer have an unbalanced current component. The final shunt result is the synthesis of the above three-component shunt. Although from the perspective of current, because the filters participating in parallel connection under the three components are not the same, the current shunt is different. Printing However, from the perspective of the three individual components, the shunt of the three components can still be controlled in accordance with the capacity limit. In addition, under the proposed parallel method, the actual operation time of each filter does not need to be coordinated, and each filter can be added or removed at any time and regardless of the order. For example, when the filter 5 closer to the power side is activated first than the filter 1 on the load side, when filter 1 is added, 18 548886 A7 B7 V. Description of the invention () (Please read the precautions on the back before (Fill in this page) The load current calculated by filter 1 is the full load current, so it will provide compensation up to its limited capacity. As soon as filter 1 provides compensation, the load current detected by filter 5 and other activated filters may change, so its compensated capacity will change to the newly calculated capacity. Figure 9 shows an example of multiple parallel sets. Two filters of the same capacity are connected in parallel to share the load. The load is unbalanced in three phases and the capacity of each component exceeds the capacity of a filter. Therefore, the load current compensated by the first filter is still unbalanced, backward and slightly distorted. After filtering by the second filter, the virtual work, harmonic current and unbalanced current of the current can be fully compensated, so the input current In order to balance, low distortion and be in phase with the voltage, the purpose of power factor is one. In summary, the parallel connection of the proposed invention has the following advantages: (1) The connection between the parallel modules without control signals can automatically achieve the average shunt, and even the shunt ratio can be planned according to the capacity of the filter. (2). The actual operation time of each filter does not need to be coordinated. The filters of the consumer cooperatives of the employees of the Intellectual Property Bureau of the Ministry of Economy can be added or removed at any time and regardless of the order. (3). Since the control of the external circuit of the proposed filter is open circuit except voltage, it has high stability, which is the first item of feasibility of the parallel system. (4). The ability of redundancy design has high fault tolerance, so the reliability of the parallel system is quite high. 19 This paper size applies the Chinese National Standard (CNS) A4 specification (210X 297 mm) 548886 A7 B7 V. Description of the invention () (5) · Low demand for filter capacity, can use IGBT with fast switching speed and high efficiency Converter. (Please read the precautions on the back before filling this page) (6). Even when the capacity of the parallel filter is lower than the load requirement, it can still operate stably and compensate for some loads. (7). Independently control the amount of distribution, will not be affected by the damage of other groups. (8). High economic efficiency makes the design capacity closer to the required capacity. [Brief description of the diagram] Fig. 1 is a conventional parallel structure of an active power filter using multiple sets of compensation for different frequency current methods. Figure 2 shows a conventional active power filter parallel architecture using multiple sets of different switching frequency methods. FIG. 3 is a circuit architecture of an active power filter according to the present invention. FIG. 4 is an architecture of an inner loop current controller of an active power filter according to the present invention. FIG. 5 is an architecture of an external loop controller of an active power filter according to the present invention. Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs. Figure 6 shows the relationship between the abc axis and the dq axis used in the active power filter of the present invention. Fig. 7 is an operation waveform of the three-phase four-wire of the active power filter of the present invention. FIG. 8 is a multi-group parallel mode and embodiment of the active power filter according to the present invention, in which there are five groups of filters of the same capacity connected in parallel, the capacity limit of which is 5KVAR of virtual work, 10A distortion current amplitude, and 1KW unbalanced power limit. One virtual work 16.5KVAR, distortion current amplitude 2 5 A, three-phase current unbalanced maximum two-phase real power difference 20 This paper size applies to China National Standard (CNS) A4 specification (210X297 mm) 548886 A7 ΒΊ_ V. Description of the invention () When the load is 1. 7KW, the compensation method of the virtual power of each filter is shown in (a), the compensation method of the harmonics of each filter is shown in (b), and the compensation method of unbalanced power of each filter As shown in (c). ............. Installation: *., (Please read the precautions on the back before filling out this page) Figure 9 shows the waveforms of two parallel operation examples of the active power filter of the present invention. Fig. 10 is an equivalent circuit of the active power filter according to the present invention at a high frequency switching frequency. In the figure, F. ·· Power filter 1 ... Load 2 .. • Converter 3. • Pulse width modulation circuit 4. • Current control circuit 5. • Compensation of virtual work latent wave current and unbalanced current Circuit 5 1. • Virtual work compensator 5 11.... Low-pass filter 52. • Harmonic current compensator 521... Band-pass filter 53 • Unbalanced current compensator 53 1. .. low-pass Filter 54 ... DC voltage regulator 541 ... Voltage controller 5 12, 522, 5 3 2 _ · Limiter Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economy 21

Claims (1)

548886 A8 B8 C8 D8 VI. Scope of patent application (please read the notes on the back before filling this page) 1 · A three-phase parallel-connected active power filter, which is one connected in parallel with the load and uses four The three-phase four-color active power filter of the arm-type voltage source converter is characterized in that the filter simultaneously compensates the load's virtual work, harmonic current, and current imbalance by means of current compensation; making the input current three-phase Balance, low distortion, in phase with input voltage, neutral current is zero, and the capacity of each component to be compensated can be limited separately, even if the filter capacity is lower than the load capacity, it can work normally to improve part of the load. 2 · The active power filter described in item 1 of the scope of patent application, the switching of the four-arm switch adopts the pulse width modulation (PWM) switching method, in which the control of the fourth arm connected to the neutral line The average of the three-phase voltages with a negative voltage divided by the voltage gain of the converter. The switching of the other three arms is like the general three-phase three-wire converter design. It does not interfere with each other. Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs3. The active power filter described in item 1 of the scope of patent application, which can be connected in parallel in multiple groups, and its multiple groups in parallel technology, which uses series load current sensing coordination The capacity of each component is limited; the capacity can be increased in parallel as the capacitor improves the power factor, and each filter does not require a control signal connection, and the current of each component can be automatically allocated according to the capacity set by the filter. 4 · The active power filter as described in item 1 of the scope of patent application, in which a small capacitor is connected in series between the neutral line of the power supply and the load; under normal operating conditions, the high-frequency switching current harmonics of most converters can be attenuated , So that the power supply neutral line is not polluted by high-frequency switching signals. _22__ This paper size applies to Chinese National Standard (CNS) A4 specification (210X297 mm) 548886 A8 B8 C8 D8 6. Application for patent scope 5. The active power filter described in item 1 of the scope of patent application, it can also be used In a three-phase three-wire system, when it is used, the system can be wired, that is, three-arm phase, four-three-phase, and three-phase. The linear power source and the province need only be saved (please read the precautions on the back before filling this page). Economy Printed by the Ministry of Intellectual Property Bureau's Consumer Cooperatives 23 This paper size applies to China National Standard (CNS) Α4 specification (210 × 297 mm)