Cascaded H-bridge energy storage system DC side current ripple suppression and frequency improvement method

Abstract

The invention provides a cascade H-bridge energy storage system DC side current ripple suppression and frequency boosting method, which comprises the steps of determining a target main frequency of DC side current ripple of a sub-module according to a switching frequency and a filtering cost of the sub-module; according to the target main frequency, determining frequency components of odd harmonics of modulation waves injected into the cascaded H-bridge battery energy storage system; according to the working insulation voltage of the cascaded H-bridge battery energy storage system, determining the maximum amplitude of the output voltage of the sub-module; determining the phase of odd harmonic of the injected modulated wave; according to the maximum amplitude of the output voltage of the sub-module, determining the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonic is injected; and inputting the modulation wave into which the odd harmonics are injected into a modulation algorithm, and determining a switching signal of the sub-module power device. According to the invention, the harmonic wave is injected into the modulation wave to effectively reduce and even eliminate the double frequency generation pulsating current at the DC side of the cascaded H-bridge battery energy storage system, and the frequency of the pulsating current at the DC side is improved, so that low-cost filtering is facilitated.

Description

Technical Field

[0001] The present disclosure relates to the technical field of battery energy storage, and in particular to a method for suppressing current pulsation and increasing frequency on a DC side of a cascaded H-bridge energy storage system. Background Art

[0002] The cascaded H-bridge battery energy storage system is suitable for high-voltage and high-power energy storage scenarios due to its high equivalent switching frequency, good output voltage harmonic characteristics, modular design, easy expansion, and convenient fault redundancy control.

[0003] Each submodule of the cascaded H-bridge battery energy storage system is a single-phase structure, and the submodule modulation wave is a power frequency sine wave. Therefore, the output power of each module is a double frequency pulsation, which inevitably causes the DC side bus current to contain a high proportion of double frequency components and switching frequency components. Among them, the switching frequency component current frequency is relatively high and easy to filter out. In order to avoid the adverse effects of double frequency current injection on the battery's life, efficiency and safety, there are currently two types of methods: passive filters and active filters.

[0004] The passive filter method is relatively low-cost, simple and reliable. Generally, an inductor and capacitor are used to form a low-pass filter or a notch filter to filter out the double frequency component in the current. Since the double frequency is only 100Hz, the frequency is relatively low, resulting in a large inductance and capacitance of the required filter, resulting in a large volume of inductors and capacitors, high cost, and difficulty in completely filtering out the double frequency component.

[0005] The active filtering method requires power devices, passive power devices, heat dissipation devices, and uses digital control, which is more expensive and less reliable. The active filtering method mainly connects the energy storage battery and the DC bus of the submodule through a bidirectional DC / DC converter. The DC / DC converter controls the size of the DC current of the energy storage battery charging and discharging according to the power demand, and the pulsating current on the DC bus of the submodule is all borne by the bus capacitor. There are also literatures that propose to connect an active filter in parallel to the DC bus of the submodule to absorb the double frequency current, but the above scheme has not yet been put into practical use.

[0006] The patent publication "High-voltage direct-mounted energy storage method and system for eliminating double-frequency current of battery charging and discharging" (publication number CN114865896A) proposes a method of injecting triple-frequency, quintuple-frequency and higher-frequency common-mode voltages into a star-connected cascaded H-bridge battery energy storage system to reduce and completely eliminate the double-frequency current on the DC side of the submodule. However, when this method is used, the maximum amplitude of the modulation voltage after injecting the triple-frequency common-mode voltage has reached twice the amplitude of the grid voltage; the maximum amplitude of the modulation voltage after injecting the quintuple-frequency common-mode voltage will reach three times the amplitude of the grid voltage; the more common-mode voltages are injected, the greater the modulation voltage required. This will lead to a significant increase in the insulation cost of the equipment and a significant reduction in the battery voltage utilization rate, and there is no feasibility of application at all.

[0007] In current practical applications, passive low-pass filters are often used to suppress the pulsation of the DC side current, but the high cost of passive filters still has a significant impact on the cost and economy of the cascaded H-bridge energy storage system. Taking low-cost measures, preferably without increasing hardware costs, to reduce or even eliminate the double frequency current of the submodule, or to convert the pulsating current on the DC side from double frequency to a higher frequency so that it is easier to filter out, has good practical significance and application value. Summary of the invention

[0008] In view of the defects in the prior art, the purpose of the present invention is to provide a method for suppressing the current pulsation and increasing the frequency of the DC side of a cascaded H-bridge energy storage system.

[0009] To achieve the above object, according to one aspect of the present disclosure, a method for suppressing current pulsation and increasing frequency on the DC side of a cascaded H-bridge energy storage system is provided, comprising:

[0010] Determining a target main frequency of a DC side current pulsation of the submodule according to a switching frequency and a filtering cost of the submodule;

[0011] Determining the frequency components of odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system according to the target main frequency of the DC side current pulsation of the submodule;

[0012] Determining the maximum amplitude of the output voltage of each submodule according to the working insulation voltage of the cascaded H-bridge battery energy storage system;

[0013] Determining the phase of the odd harmonics of the modulated wave injected into the cascaded H-bridge battery energy storage system;

[0014] Determine, according to the maximum amplitude of the output voltage of each submodule, a modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics;

[0015] The modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected is input into a preset modulation algorithm to determine the switching signal of the sub-module power device.

[0016] Optionally, determining the target main frequency of the DC side current pulsation of the submodule according to the switching frequency and filtering cost of the submodule includes:

[0017] According to the switching frequency and filtering cost of the submodule, the target main frequency of the DC side current pulsation of the submodule is determined to be an even multiple of the power frequency and not greater than the maximum value of the switching frequency of the submodule.

[0018] Optionally, the frequency components of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system include all odd harmonics with a harmonic order smaller than that corresponding to the target main frequency of the DC side current pulsation of the submodule.

[0019] Optionally, the method further comprises:

[0020] According to the rated voltage of the cascaded H-bridge battery energy storage system, it is determined that the working insulation voltage of the cascaded H-bridge battery energy storage system is K times the rated voltage.

[0021] Optionally, determining the maximum amplitude of the output voltage of each submodule according to the working insulation voltage of the cascaded H-bridge battery energy storage system includes:

[0022] According to the operating insulation voltage of the cascaded H-bridge battery energy storage system being K times the rated voltage, it is determined that the maximum amplitude of the output voltage of each submodule is K times the rated voltage amplitude of each submodule.

[0023] Optionally, determining the phase of the odd harmonics of the modulated wave injected into the cascaded H-bridge battery energy storage system includes:

[0024] Taking the phase of the fundamental sine wave of the modulating wave as a reference and according to the expression of the fundamental current of the grid-connected power frequency, determining the expression of the odd harmonics of the modulating wave injected into the cascaded H-bridge battery energy storage system;

[0025] According to the expression of the odd harmonics of the modulated wave injected into the cascaded H-bridge battery energy storage system, the phase of the odd harmonics is determined.

[0026] Optionally, determining the modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics according to the maximum amplitude of the output voltage of each submodule includes:

[0027] According to K times the rated voltage amplitude of each submodule, when the grid-connected current of the cascaded H-bridge battery energy storage system and the fundamental wave of the modulation wave are in different phases, an over-limit cutoff method is used to determine the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected;

[0028] According to K times the rated voltage amplitude of each of the submodules, when the grid-connected current of the cascaded H-bridge battery energy storage system and the fundamental wave of the modulation wave are in the same phase, a calculation method based on the over-limit cutoff method is used to determine the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected.

[0029] Optionally, according to K times the rated voltage amplitude of each of the submodules, when the grid-connected current of the cascaded H-bridge battery energy storage system and the fundamental wave of the modulation wave are in different phases, an over-limit cutoff method is used to determine the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected, including:

[0030] Setting the harmonic amplitudes of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system to be the same as the power frequency fundamental wave of the modulation wave;

[0031] Determine a premodulation wave for injecting odd harmonics according to the harmonic amplitude of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system and each odd harmonic;

[0032] If the pre-modulated wave injected with the odd harmonics is not greater than K times the rated voltage amplitude of the submodule, determine that the modulation value of the modulation wave of the cascaded H-bridge battery energy storage system after the injection of the odd harmonics is the pre-modulated wave injected with the odd harmonics;

[0033] If the pre-modulated wave injected with odd harmonics is greater than K times the rated voltage amplitude of the submodule, determine that the modulation value of the modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics is K times the rated voltage amplitude of the submodule.

[0034] Optionally, according to K times the rated voltage amplitude of each of the submodules, when the grid-connected current of the cascaded H-bridge battery energy storage system and the fundamental wave of the modulation wave are in the same phase, a calculation method based on an over-limit cutoff method is used to determine the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected, including:

[0035] Performing Fourier decomposition processing on the modulated wave of the cascaded H-bridge battery energy storage system after the injection of the odd harmonics determined by the over-limit truncation method, to determine the actual amplitude of each odd harmonic;

[0036] According to the actual amplitude of each odd harmonic, the modulation value of the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonic is injected is determined.

[0037] Compared with the prior art, the embodiments of the present disclosure have at least one of the following beneficial effects:

[0038] Through the above technical solution, odd harmonics are injected into the modulation wave of the cascaded H-bridge battery energy storage system, frequency aliasing is generated in the DC side current, and the current pulsation is moved from low frequency to high frequency, thereby transferring the frequency of the double-frequency pulsating current on the DC side to a higher frequency, thereby reducing or even eliminating the double-frequency pulsating current on the DC side of the cascaded H-bridge battery energy storage system at a lower cost. The working insulation voltage of the cascaded H-bridge battery energy storage system is taken into consideration, and the elimination effect of the double-frequency current on the DC side is optimized at a lower cost while ensuring the insulation safety of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Other features, objects and advantages of the present disclosure will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0040] Figure 1 It is a flow chart of a method for suppressing current ripple and increasing frequency on the DC side of a cascaded H-bridge energy storage system according to an exemplary embodiment.

[0041] Figure 2 The figure is a schematic diagram of a topological structure of a cascaded H-bridge battery energy storage system according to an exemplary embodiment.

[0042] Figure 3 It is a schematic diagram of simulation waveforms of a cascaded H-bridge battery energy storage system in which the sub-module modulation voltage is normalized according to the fundamental wave using a calculation method according to an exemplary embodiment.

[0043] Figure 4 The figure is a schematic diagram of a submodule DC side current simulation waveform of a cascaded H-bridge battery energy storage system using a calculation method according to an exemplary embodiment.

[0044] Figure 5 It is a schematic diagram of a spectrum of a submodule DC side current normalized according to a fundamental wave of a cascaded H-bridge battery energy storage system using a calculation method according to an exemplary embodiment.

[0045] Figure 6 It is a schematic diagram of simulation waveforms of a cascaded H-bridge battery energy storage system using an over-limit cutoff method and normalizing the sub-module modulation voltage according to the fundamental wave according to an exemplary embodiment.

[0046] Figure 7 The diagram is a schematic diagram of a submodule DC side current simulation waveform of a cascaded H-bridge battery energy storage system using an over-limit cutoff method according to an exemplary embodiment.

[0047] Figure 8 The diagram is a schematic diagram of a spectrum of a submodule DC side current normalized according to a fundamental wave in a cascaded H-bridge battery energy storage system using an over-limit cutoff method according to an exemplary embodiment. DETAILED DESCRIPTION

[0048] The present disclosure is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present disclosure, but are not intended to limit the present disclosure in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present disclosure. These all fall within the scope of protection of the present disclosure.

[0049] Figure 1 The present invention is a flow chart showing a method for suppressing DC ripple and increasing frequency of a cascaded H-bridge battery energy storage system according to an exemplary embodiment.

[0050] like Figure 1 As shown, the present disclosure provides a method for suppressing current ripple and increasing frequency on the DC side of a cascaded H-bridge energy storage system, including S11 to S16.

[0051] S11, determining a target main frequency of the DC side current pulsation of the submodule according to the switching frequency and filtering cost of the submodule.

[0052] In the present disclosure, the cascaded H-bridge battery energy storage system is a cascaded H-bridge energy storage system.

[0053] Among them, in the cascade H-bridge battery energy storage system, its sub-modules mostly use carrier phase-shift modulation, and the switching frequency of each sub-module is the same.

[0054] The DC side of the cascaded H-bridge battery energy storage system uses passive LC filtering. The lower the filtered frequency, the larger the required inductance L and capacitance C, and the higher the filtering cost of the filter.

[0055] S12, determining the frequency components of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system according to the target main frequency of the DC side current pulsation of the submodule.

[0056] S13, determining the maximum amplitude of the output voltage of each submodule according to the working insulation voltage of the cascaded H-bridge battery energy storage system.

[0057] S14, determining the phase of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system.

[0058] S15, determining a modulation wave of the cascaded H-bridge battery energy storage system after odd harmonics are injected according to the maximum amplitude of the output voltage of each submodule.

[0059] S16, inputting the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected into the modulation algorithm to determine the switching signal of the sub-module power device.

[0060] Among them, its modulation algorithm can adopt carrier phase shift modulation method, carrier stacking modulation method and nearest level modulation method.

[0061] In a possible embodiment, the submodule power device is controlled according to the determined switching signal of the submodule power device to achieve DC ripple suppression and frequency increase of the cascaded H-bridge battery energy storage system, thereby reducing or completely eliminating the double frequency current on the DC side of the submodule.

[0062] Through the above technical solution, odd harmonics are injected into the modulation wave of the cascaded H-bridge battery energy storage system, frequency aliasing is generated in the DC side current, and the current pulsation is moved from low frequency to high frequency, thereby transferring the frequency of the double-frequency pulsating current on the DC side to a higher frequency, thereby reducing or even eliminating the double-frequency pulsating current on the DC side of the cascaded H-bridge battery energy storage system at a lower cost. The working insulation voltage of the cascaded H-bridge battery energy storage system is taken into consideration, and the elimination effect of the double-frequency current on the DC side is optimized at a lower cost while ensuring the insulation safety of the system.

[0063] In a possible embodiment, S11 may include:

[0064] According to the switching frequency and filtering cost of the submodule, the target main frequency of the DC side current pulsation of the submodule is determined to be an even multiple of the power frequency and not greater than the maximum value of the switching frequency of the submodule.

[0065] Among them, the target main frequency of the DC side current pulsation of the submodule is an even multiple of the industrial frequency. Under the premise of not exceeding the switching frequency of the submodule, a higher target main frequency is selected as much as possible to reduce the filtering cost of the submodule.

[0066] In a possible embodiment, the frequency components of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system in step S12 include all odd harmonics whose harmonic orders are smaller than the target main frequency of the DC side current pulsation of the submodule.

[0067] In a possible embodiment, a method for suppressing current pulsation and increasing frequency on the DC side of a cascaded H-bridge energy storage system further includes S17.

[0068] S17, according to the rated voltage of the cascaded H-bridge battery energy storage system, determining that the working insulation voltage of the cascaded H-bridge battery energy storage system is K times the rated voltage.

[0069] Among them, according to the requirements of high voltage ride-through of the cascaded H-bridge battery energy storage system and considering the impact of reinforced insulation on cost, the long-term withstanding working insulation voltage of the cascaded H-bridge battery energy storage system is K times the rated voltage of the cascaded H-bridge battery energy storage system, where the value range of K is [1.1, 2.0].

[0070] In a possible embodiment, S13 may include:

[0071] According to the operating insulation voltage of the cascaded H-bridge battery energy storage system being K times the rated voltage, the maximum amplitude of the output voltage of each submodule is determined to be K times the rated voltage amplitude of each submodule.

[0072] Among them, the rated voltage amplitude of each submodule is expressed as U peak , the value range of K is [1.1, 2.0], and the maximum limit of the output voltage amplitude of each submodule is K·U peak , and the maximum amplitude of the output voltage of each submodule is within the operating range of the submodule battery cluster.

[0073] In a possible embodiment, S14 may include S21 to S22.

[0074] S21, taking the phase of the fundamental sine wave of the modulating wave as a reference and according to the expression of the fundamental current of the grid-connected power frequency, determining the expression of the odd harmonics of the modulating wave injected into the cascaded H-bridge battery energy storage system.

[0075] Among them, the phase of the modulating wave sinusoidal power frequency fundamental wave is set to 0, and the expression of the modulating wave sinusoidal power frequency fundamental wave is:

[0076] u 1M =A1·sin(ωt)

[0077] Among them, u 1M It represents the instantaneous value of the power frequency fundamental wave of the modulated wave, 1 represents the power frequency fundamental wave, M represents the modulated wave, A1 represents the power frequency fundamental wave amplitude of the modulated wave, ω represents the power frequency angular frequency, and t represents time.

[0078] The expression of grid-connected power frequency fundamental current is:

[0079]

[0080] Among them, i1 represents the grid-connected power frequency fundamental current, B1 represents the power frequency fundamental amplitude of the grid-connected current, It indicates the electrical angle of the grid-connected power frequency fundamental current lagging behind the modulated power frequency fundamental current.

[0081] Therefore, the expression of the third harmonic of the injected modulated wave is:

[0082]

[0083] Where A3 represents the third harmonic amplitude, Indicates the phase of the third harmonic relative to the fundamental wave.

[0084] The expression for the fifth harmonic of the injected modulated wave is:

[0085]

[0086] Among them, A5 represents the fifth harmonic amplitude, Indicates the phase of the fifth harmonic relative to the fundamental wave.

[0087] The expression for the seventh harmonic of the injected modulated wave is:

[0088]

[0089] Among them, A7 represents the seventh harmonic amplitude, Indicates the phase of the seventh harmonic relative to the fundamental wave.

[0090] The expression for the ninth harmonic of the injected modulated wave is:

[0091]

[0092] Among them, A9 represents the ninth harmonic amplitude, Indicates the phase of the ninth harmonic relative to the fundamental wave.

[0093] By analogy, the expression of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system is:

[0094]

[0095] Among them, u nM represents the nth harmonic of the injected modulated wave, Indicates the phase of the nth harmonic, A n represents the amplitude of the nth harmonic, ω represents the angular frequency of the power frequency, It indicates the electrical angle of the grid-connected power frequency fundamental current lagging behind the modulated power frequency fundamental current.

[0097] S22, determining the phase of the odd harmonics according to an expression of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system.

[0098] Among them, the expression of the odd harmonics of the modulated wave injected into the cascaded H-bridge battery energy storage system can be analogized to the highest harmonic of the modulated wave injected into the cascaded H-bridge battery energy storage system, and the phase of each odd harmonic is determined based on the expression of each odd harmonic.

[0099] In a possible embodiment, S15 may include S31 and S32.

[0100] S31, according to K times the rated voltage amplitude of each submodule, when the grid-connected current of the cascaded H-bridge battery energy storage system and the fundamental wave of the modulation wave are in different phases, an over-limit cutoff method is used to determine the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected;

[0101] S32, according to K times the rated voltage amplitude of each submodule, when the grid-connected current of the cascaded H-bridge battery energy storage system and the fundamental wave of the modulation wave are in the same phase, a calculation method based on the over-limit cutoff method is used to determine the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected.

[0102] In a possible embodiment, S31 may include S301 to S304.

[0103] S301, setting the harmonic amplitudes of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system to be the same as the industrial frequency fundamental wave of the modulation wave.

[0104] The harmonic amplitudes of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system are preset to be the same as the industrial frequency fundamental wave of the modulation wave, which is A1.

[0105] S302, determining a pre-modulated wave for injecting odd harmonics according to the harmonic amplitude of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system and each odd harmonic.

[0106] The expression of the premodulation wave injected with odd harmonics is:

[0107]

[0108] Among them, u pre-M It represents the pre-modulated wave injected with odd harmonics, and N represents the highest odd harmonic number injected.

[0109] S303: If the pre-modulated wave injected with the odd harmonics is not greater than K times the rated voltage amplitude of the submodule, determine that the modulation value of the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected is the pre-modulated wave injected with the odd harmonics.

[0110] Among them, if the premodulation value u pre-M ≤K·U peak , then the modulation value u M =u pre-M .

[0111] S304: If the pre-modulated wave injected with the odd harmonics is greater than K times the rated voltage amplitude of the submodule, determine that the modulation value of the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected is K times the rated voltage amplitude of the submodule.

[0112] Among them, if the pre-modulation value u pre-M >K.U peak , then the modulation value u M =K·U peak .

[0113] When using the calculation method, the over-limit truncation method needs to be used as a basis.

[0114] In a possible embodiment, S32 includes S301 to S306.

[0115] S305, performing Fourier decomposition processing on the modulation wave of the cascaded H-bridge battery energy storage system after the injection of odd harmonics determined by the over-limit truncation method, to determine the actual amplitude of each odd harmonic.

[0116] Among them, the modulation wave u of the cascaded H-bridge battery energy storage system after injecting odd harmonics is obtained. M Perform Fourier decomposition, that is, the third, fifth, seventh, ninth, and even Nth odd harmonics u 3M 、u 5M 、u 7M 、u 9M ,...,u NM , determine the actual amplitude of each odd harmonic, denoted as: A'1, A'3, A'5, A'7, A'9, ..., A' N .

[0117] S306, determining the modulation value of the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected according to the actual amplitude of each odd harmonic.

[0118] Recalculate the modulation value of the modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics. The expression is as follows:

[0119]

[0120] Among them, u M It is represented by the modulation value of the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected, A' n Indicates the actual amplitude of the nth odd harmonic.

[0121] Among them, steps S301 to S304 can refer to the above steps and will not be repeated here.

[0122] Figure 2 The figure is a schematic diagram of a topological structure of a cascaded H-bridge battery energy storage system according to an exemplary embodiment.

[0123] In a possible embodiment, Figure 2 As shown, a cascade H-bridge energy storage system has a rated voltage of 10kV, a rated phase current peak of 100A, each phase includes N=16 submodules, and the entire cascade H-bridge energy storage system includes 48 submodules. The rated voltage peak of each submodule is 510V, the nominal voltage of each submodule battery cluster is 768V, the operating voltage range is 672-840V, and the corresponding modulation ratio is 0.61-0.76. The submodule switching frequency is 1kHz.

[0124] In this embodiment, carrier phase shift modulation is adopted.

[0125] The cascaded H-bridge battery energy storage system can operate in a pure active state, a pure reactive state, or a state of outputting both active and reactive power. The following two cases are used as examples for explanation.

[0126] Figure 3 It is a schematic diagram of simulation waveforms of a cascaded H-bridge battery energy storage system in which the sub-module modulation voltage is normalized according to the fundamental wave using a calculation method according to an exemplary embodiment. Figure 4 The figure is a schematic diagram of a submodule DC side current simulation waveform of a cascaded H-bridge battery energy storage system using a calculation method according to an exemplary embodiment. Figure 5 It is a schematic diagram of a spectrum of a submodule DC side current normalized according to a fundamental wave of a cascaded H-bridge battery energy storage system using a calculation method according to an exemplary embodiment.

[0127] As an example, in the first case, the grid-connected current of the cascaded H-bridge battery energy storage system is in phase with the fundamental wave of the modulation wave.

[0128] The specific process is as follows:

[0129] Step 1: The switching frequency of the submodule is 1kHz. In order to ensure the switching modulation effect of the submodule power device while moving the DC side current pulsation to a high frequency, the target frequency is determined to be 5 times the double frequency, that is, 500Hz.

[0130] Step 2: Determine that the frequency components of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system are the third harmonic, the fifth harmonic, the seventh harmonic, and the ninth harmonic.

[0131] Step 3: According to the high voltage ride-through requirements of the cascaded H-bridge battery energy storage system, the cascaded H-bridge battery energy storage system used in the medium voltage power grid should be able to withstand a voltage not less than 1.3 times the rated voltage for a long time. While retaining an appropriate safety margin, K is taken as 1.25, and the maximum amplitude of the output voltage of each submodule is determined to be 1.25 times the rated voltage amplitude of the submodule, that is, the maximum amplitude of the submodule output voltage is 637.5V, which is within the nominal voltage of the submodule battery cluster of 768V.

[0132] Step 4: Calculate the phase of each odd harmonic of the modulation wave injected into the cascaded H-bridge battery energy storage system:

[0133] Taking the phase of the modulating wave sinusoidal power frequency fundamental wave as the reference and assuming its phase is 0, the expression of the modulating wave sinusoidal power frequency fundamental wave is:

[0134] u 1M =510·sin(ωt)

[0135] The expression of grid-connected power frequency fundamental current is:

[0136] i1=100·sin(ωt)

[0137] Then the expression of the third harmonic of the injected modulated wave is:

[0138] u 3M =A3·sin(3ωt)

[0139] The expression for the fifth harmonic of the injected modulated wave is:

[0140] u 5M =A5·sin(5ωt)

[0141] The expression for the seventh harmonic of the injected modulated wave is:

[0142] u 7M =A7·sin(7ωt)

[0143] The expression for the ninth harmonic of the injected modulated wave is:

[0144] u 9M =A9·sin(9ωt)

[0145] Step 5: Calculate the modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics using a calculation method based on the over-limit cutoff method:

[0146] The harmonic amplitudes of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system are set to be the same as the industrial frequency fundamental wave of the modulation wave, both of which are 510V.

[0147] Generate a premodulated wave with odd harmonics injected:

[0148]

[0149] The pre-modulated wave u pre-M The voltage is compared with K times the rated voltage amplitude of the submodule, i.e. 637.5V (=1.25·510V), and the over-limit cutoff is performed to obtain the modulation wave u of the cascaded H-bridge battery energy storage system after the odd harmonic injection after the cutoff. M The modulation value is:

[0150]

[0151] For the determined truncated modulation wave u M Fourier decomposition was performed to determine the actual amplitudes of the third, fifth, seventh, and ninth harmonics, which were 0.350, 0.235, 0.257, and 0.377 times the amplitude of the fundamental wave, respectively.

[0152] Recalculate the actual modulation value u of the modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonicsM :

[0153] u M =510*[sin(ωt)+0.350*sin(3ωt)+0.235*sin(5ωt)+0.257*sin(7ωt)+0.377*sin(9ωt)]

[0154] Step 6: Input the recalculated modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics into the carrier phase shift modulation algorithm, and output the switching signal of the sub-module power device.

[0155] like Figures 3 to 5 As shown, they are respectively a simulation waveform of the sub-module modulation voltage normalized according to the fundamental wave of the cascaded H-bridge battery energy storage system using the calculation method, a simulation waveform of the DC side current of the sub-module of the cascaded H-bridge battery energy storage system using the calculation method, and a spectrum of the DC side current of the sub-module of the cascaded H-bridge battery energy storage system using the calculation method normalized according to the fundamental wave.

[0156] Depend on Figures 3 to 5 As shown, the DC ripple suppression and frequency enhancement method of the cascaded H-bridge battery energy storage system proposed in the present disclosure can conveniently suppress the double frequency current ripple amplitude and increase the DC side current ripple frequency, thereby achieving fluctuation filtering.

[0157] Figure 6 It is a schematic diagram of simulation waveforms of a cascaded H-bridge battery energy storage system using an over-limit cutoff method and normalizing the sub-module modulation voltage according to the fundamental wave according to an exemplary embodiment. Figure 7 The diagram is a schematic diagram of a submodule DC side current simulation waveform of a cascaded H-bridge battery energy storage system using an over-limit cutoff method according to an exemplary embodiment. Figure 8 The diagram is a schematic diagram of a spectrum of a submodule DC side current normalized according to a fundamental wave in a cascaded H-bridge battery energy storage system using an over-limit cutoff method according to an exemplary embodiment.

[0158] As another example, in the second case, the grid-connected current of the cascaded H-bridge battery energy storage system is out of phase with the fundamental wave of the modulation wave.

[0159] The specific process is as follows:

[0160] Step 1: The switching frequency of the submodule is 1kHz. In order to ensure the switching modulation effect of the submodule power device while moving the DC side current pulsation to a high frequency, the target frequency is determined to be 5 times the double frequency, that is, 500Hz.

[0161] Step 2: Determine that the frequency components of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system are the third harmonic, the fifth harmonic, the seventh harmonic, and the ninth harmonic.

[0162] Step 3: According to the high voltage ride-through requirements of the cascaded H-bridge battery energy storage system, the cascaded H-bridge battery energy storage system used in the medium voltage power grid should be able to withstand a voltage not less than 1.3 times the rated voltage for a long time. While retaining an appropriate safety margin, K is taken as 1.25, and the maximum amplitude of the output voltage of each submodule is determined to be 1.25 times the rated voltage amplitude of the submodule, that is, the maximum amplitude of the submodule output voltage is 637.5V, which is within the nominal voltage of the submodule battery cluster of 768V.

[0163] Step 4: Calculate the phase of each odd harmonic of the modulation wave injected into the cascaded H-bridge battery energy storage system:

[0164] Taking the phase of the modulating wave sinusoidal power frequency fundamental wave as the reference and assuming its phase is 0, the expression of the modulating wave sinusoidal power frequency fundamental wave is:

[0165] u 1M =510·sin(ωt)

[0166] The expression of grid-connected power frequency fundamental current is:

[0167] i1=100·sin(ωt-π / 4)

[0168] Then the expression of the third harmonic of the injected modulated wave is:

[0169] u 3M =A3·sin(3ωt-π / 2)

[0170] The expression for the fifth harmonic of the injected modulated wave is:

[0171] u 5M =A5·sin(5ωt-π)

[0172] The expression for the seventh harmonic of the injected modulated wave is:

[0173] u 7M =A7·sin(7ωt-3π / 2)

[0174] The expression for the ninth harmonic of the injected modulated wave is:

[0175] u 9M =A9·sin(9ωt-2π)

[0176] Step 5: Use the over-limit truncation method to calculate the modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics:

[0177] The harmonic amplitudes of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system are set to be the same as the industrial frequency fundamental wave of the modulation wave, both of which are 510V.

[0178] Generate a premodulated wave with odd harmonics injected:

[0179]

[0180] The pre-modulated wave u pre-M The voltage is compared with K times the rated voltage amplitude of the submodule, i.e. 637.5V (=1.25·510V), and the over-limit cutoff is performed to obtain the modulation wave u of the cascaded H-bridge battery energy storage system after the odd harmonic injection after the cutoff. M The actual modulation value is:

[0181]

[0182] Step 6: Input the recalculated modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics into the carrier phase shift modulation algorithm, and output the switching signal of the sub-module power device.

[0183] like Figures 6 to 8 As shown, they are respectively the simulation waveform of the sub-module modulation voltage normalized according to the fundamental wave of the cascaded H-bridge battery energy storage system using the over-limit truncation method, the simulation waveform of the DC side current of the sub-module of the cascaded H-bridge battery energy storage system using the over-limit truncation method, and the spectrum of the DC side current of the sub-module of the cascaded H-bridge battery energy storage system using the over-limit truncation method normalized according to the fundamental wave.

[0184] Depend on Figures 6 to 8 As shown, the method for suppressing the DC side current pulsation and increasing the frequency of the cascaded H-bridge energy storage system proposed in the present disclosure can conveniently suppress the double frequency current pulsation amplitude and increase the DC side current pulsation frequency, thereby filtering the DC side current pulsation.

[0185] Through the above technical scheme, by injecting a certain component of odd harmonics of different frequencies into the sub-module modulation voltage of the star-type cascaded H-bridge battery energy storage system, it is possible to easily achieve the significant reduction of the double frequency current pulsation on the DC side while generating frequency aliasing in the DC side current, so that the DC side current pulsation moves from low frequency to high frequency, and the main frequency of the DC side current pulsation moves from double frequency to sextuple frequency, octuple frequency, ten times frequency or higher even multiple frequency, so that it can be easily filtered out at low cost.

[0186] The above describes the specific embodiments of the present disclosure. It should be understood that the present disclosure is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present disclosure. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A method for suppressing current pulsation and increasing frequency on the DC side of a cascaded H-bridge energy storage system, characterized in that: include: Determining a target main frequency of a DC side current pulsation of the submodule according to a switching frequency and a filtering cost of the submodule; Determining the frequency components of odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system according to the target main frequency of the DC side current pulsation of the submodule; Determining the maximum amplitude of the output voltage of each submodule according to the working insulation voltage of the cascaded H-bridge battery energy storage system; Determining the phase of the odd harmonics of the modulated wave injected into the cascaded H-bridge battery energy storage system; Determine, according to the maximum amplitude of the output voltage of each submodule, a modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics; The modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected is input into a preset modulation algorithm to determine the switching signal of the sub-module power device.

2. The method according to claim 1, characterized in that The step of determining the target main frequency of the DC side current pulsation of the submodule according to the switching frequency and filtering cost of the submodule includes: According to the switching frequency and filtering cost of the submodule, the target main frequency of the DC side current pulsation of the submodule is determined to be an even multiple of the power frequency and not greater than the maximum value of the switching frequency of the submodule.

3. The method according to claim 1, characterized in that: The frequency components of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system include all odd harmonics with an order smaller than that corresponding to the target main frequency of the DC side current pulsation of the submodule.

4. The method according to claim 1, characterized in that: The method further comprises: According to the rated voltage of the cascaded H-bridge battery energy storage system, it is determined that the working insulation voltage of the cascaded H-bridge battery energy storage system is K times the rated voltage.

5. The method according to claim 4, characterized in that Determining the maximum amplitude of the output voltage of each submodule according to the working insulation voltage of the cascaded H-bridge battery energy storage system includes: According to the operating insulation voltage of the cascaded H-bridge battery energy storage system being K times the rated voltage, it is determined that the maximum amplitude of the output voltage of each submodule is K times the rated voltage amplitude of each submodule.

6. The method according to claim 1, characterized in that Determining the phase of the odd harmonics of the modulated wave injected into the cascaded H-bridge battery energy storage system includes: Taking the phase of the fundamental sine wave of the modulating wave as a reference and according to the expression of the fundamental current of the grid-connected power frequency, determining the expression of the odd harmonics of the modulating wave injected into the cascaded H-bridge battery energy storage system; According to the expression of the odd harmonics of the modulated wave injected into the cascaded H-bridge battery energy storage system, the phase of the odd harmonics is determined.

7. The method according to claim 6, characterized in that The expression of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system is: Among them, u nM represents the nth harmonic injected into the modulated wave, Indicates the phase of the nth harmonic, A n represents the amplitude of the nth harmonic, ω represents the angular frequency of the power frequency, It indicates the electrical angle of the grid-connected power frequency fundamental current lagging behind the modulated power frequency fundamental current.

8. The method according to claim 5, characterized in that The method of determining the modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics according to the maximum amplitude of the output voltage of each submodule comprises: According to K times the rated voltage amplitude of each submodule, when the grid-connected current of the cascaded H-bridge battery energy storage system and the fundamental wave of the modulation wave are in different phases, an over-limit cutoff method is used to determine the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected; According to K times the rated voltage amplitude of each of the submodules, when the grid-connected current of the cascaded H-bridge battery energy storage system and the fundamental wave of the modulation wave are in the same phase, a calculation method based on the over-limit cutoff method is used to determine the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonics are injected.

9. The method according to claim 8, characterized in that The method of determining the modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics by using an over-limit cutoff method when the grid-connected current of the cascaded H-bridge battery energy storage system and the fundamental wave of the modulation wave are in different phases according to K times the rated voltage amplitude of each submodule comprises: Setting the harmonic amplitudes of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system to be the same as the power frequency fundamental wave of the modulation wave; Determine a premodulation wave for injecting odd harmonics according to the harmonic amplitude of the odd harmonics of the modulation wave injected into the cascaded H-bridge battery energy storage system and each odd harmonic; If the pre-modulated wave injected with the odd harmonics is not greater than K times the rated voltage amplitude of the submodule, determine that the modulation value of the modulation wave of the cascaded H-bridge battery energy storage system after the injection of the odd harmonics is the pre-modulated wave injected with the odd harmonics; If the pre-modulated wave injected with odd harmonics is greater than K times the rated voltage amplitude of the submodule, determine that the modulation value of the modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics is K times the rated voltage amplitude of the submodule.

10. The method according to claim 9, characterized in that The method of determining the modulation wave of the cascaded H-bridge battery energy storage system after injecting odd harmonics by using a calculation method based on an over-limit cutoff method when the grid-connected current of the cascaded H-bridge battery energy storage system and the fundamental wave of the modulation wave are in the same phase according to K times the rated voltage amplitude of each of the submodules, includes: Performing Fourier decomposition processing on the modulated wave of the cascaded H-bridge battery energy storage system after the injection of the odd harmonics determined by the over-limit truncation method, to determine the actual amplitude of each odd harmonic; According to the actual amplitude of each odd harmonic, the modulation value of the modulation wave of the cascaded H-bridge battery energy storage system after the odd harmonic is injected is determined.

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