New energy medium voltage direct current collection system and method based on adjustable direct current voltage

Abstract

The application discloses a new energy medium-voltage direct-current collection system and method based on adjustable direct-current voltage, and the topology structure of the system comprises N new energy power generation units, N isolation DC / DC converters, N mechanical bypass switches and a collection converter. Each new energy power generation unit is connected in series after being converted by a first-stage isolation DC / DC converter, and new energy direct power supply application or new energy sending-out is realized by connecting a DC / DC step-down or step-up collection converter. The collection converter adopts constant current control and has a wide input voltage range. The output voltage of the corresponding isolation DC / DC converter can be adjusted to adapt to the change of the output power of each new energy power generation unit. The new energy medium-voltage direct-current collection method has the advantages of avoiding power loss, low design difficulty and cost of the isolation DC / DC converter, low cable cost, small current stress, low voltage ratio of the collection converter, flexible switching and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of power electronics, and relates to a new energy medium-voltage direct-current collection system and method, in particular to a new energy medium-voltage direct-current collection system and method based on an adjustable direct-current voltage. BACKGROUND

[0002] With the proposal of the double carbon strategy, the way of generating electricity by using renewable energy such as solar energy and wind energy has developed rapidly. Unlike fossil energy, new energy power generation has the characteristics of instability, low inertia, scattered distribution and intermittent power generation, and how to economically and efficiently collect and transmit energy is a key problem. The new energy full direct-current collection and transmission scheme with a medium-voltage series structure has the advantages of low cost, high efficiency, simple structure and no need for high-voltage-ratio collection converters, and has a good development prospect.

[0003] The direct-current collection bus voltage of the existing new energy series direct-current collection scheme is fixed, and the output voltage of the power generation unit is coupled with the power. In the working condition where the output of each power generation unit is greatly different, high output means that the output voltage needs to be much higher than the rated voltage, which will be limited by the voltage output capability of the DC / DC converter of the power generation unit, and it is difficult to ensure that each wind turbine or photovoltaic can realize MPPT operation, greatly reducing the power output capability of the new energy power plant. The series collection scheme with a series-parallel structure requires a DC / DC converter with a wide voltage boosting range, which is difficult to design and control.

[0004] In view of the above problems, CN116014785A proposes a direct-current collection scheme in which wind turbines are first connected in series to form wind turbine clusters, and then the wind turbine clusters are connected in parallel. The position distribution of a cluster of wind turbines can be optimized to avoid too large output power difference between wind turbines, and the number of series wind turbines is reduced to reduce the voltage boosting requirement of the wind turbine DC / DC converter. This scheme cannot fundamentally solve the coupling of the output voltage between wind turbines, and the wind curtailment problem is still serious, which reduces the economy of the series scheme. CN111416371A proposes an energy storage control system for a series photovoltaic direct-current collection system, which realizes active compensation and suppression of mismatched power in the system through a real-time communication system in the station, and can significantly improve the system operation capability under wide-range power fluctuation conditions. This scheme requires high-speed communication interconnection between each power generation unit and the collection unit, which greatly increases the construction cost and difficulty, and is not suitable for long-distance collection scenarios.

[0005] In summary, in order to fully exert the many advantages of the series scheme, a new series collection scheme that is economical and efficient and can always maintain MPPT operation of the new energy power generation unit is needed. SUMMARY

[0006] In view of the above-mentioned deficiencies of the prior art, the present application provides a new energy medium voltage DC collection system and method based on adjustable DC voltage, each new energy generating unit is connected in series after being converted by a first isolation DC / DC converter, and a DC / DC step-down or step-up collection converter is connected to realize new energy direct power supply application or new energy sending out, the collection converter adopts constant current control and has a wide input voltage range, and each new energy generating unit can adapt to the change of its output power by adjusting the output voltage of the corresponding isolation DC / DC converter. The present application has the characteristics of DC collection voltage self-adaptation, adjustable series current, operation control decoupling between generating units, high efficiency and low cost.

[0007] The object of the present application is achieved by the following technical solutions:

[0008] A new energy medium voltage DC collection system based on adjustable DC voltage, the topological structure of which comprises N new energy generating units, N isolation DC / DC converters, N mechanical bypass switches and a collection converter, wherein:

[0009] The N new energy generating units each comprise a positive terminal and a negative terminal;

[0010] The N isolation DC / DC converters each comprise a generating side and a collection side, wherein the generating side comprises a positive terminal and a negative terminal, and the collection side comprises a positive terminal and a negative terminal;

[0011] The N mechanical bypass switches each comprise a positive terminal and a negative terminal;

[0012] The collection converter comprises a collection side and a delivery side, wherein the collection side comprises a positive terminal and a negative terminal, and the delivery side comprises a positive terminal and a negative terminal;

[0013] The N new energy generating units and the N isolation DC / DC converters are paired one by one and connected in the same way, that is, the positive terminal of the new energy generating unit is connected to the positive terminal of the generating side of the isolation DC / DC converter, and the negative terminal of the new energy generating unit is connected to the negative terminal of the generating side of the isolation DC / DC converter;

[0014] The N isolation DC / DC converters and the N mechanical bypass switches are paired one by one and connected in the same way, that is, the positive terminal of the collection side of the isolation DC / DC converter is connected to the positive terminal of the mechanical bypass switch, and the negative terminal of the collection side of the isolation DC / DC converter is connected to the negative terminal of the mechanical bypass switch;

[0015] The N isolated DC / DC converters are connected in series in turn and connected with the collection converter, and the specific connection mode is that the positive terminal of the collection side of the first isolated DC / DC converter is connected with the positive terminal of the collection side of the collection converter, the negative terminal of the collection side of the Nth isolated DC / DC converter is connected with the negative terminal of the collection side of the collection converter, and the negative terminal of the collection side of the nth (n = 1, 2, 3, …, N-1) isolated DC / DC converter is connected with the positive terminal of the collection side of the (n+1)th isolated DC / DC converter.

[0016] A new energy medium voltage DC collection method based on adjustable DC voltage, comprising the following steps:

[0017] Step one, design the topology structure of the new energy medium voltage DC collection system based on adjustable DC voltage

[0018] The topology structure of the new energy medium voltage DC collection system based on adjustable DC voltage comprises N new energy generating units, N isolated DC / DC converters, N mechanical bypass switches and a collection converter, wherein:

[0019] The N new energy generating units each comprise a positive terminal and a negative terminal;

[0020] The N isolated DC / DC converters each comprise a generating side and a collection side, wherein the generating side each comprises a positive terminal and a negative terminal, and the collection side each comprises a positive terminal and a negative terminal;

[0021] The N mechanical bypass switches each comprise a positive terminal and a negative terminal;

[0022] The collection converter comprises a collection side and a delivery side, wherein the collection side comprises a positive terminal and a negative terminal, and the delivery side comprises a positive terminal and a negative terminal;

[0023] The N new energy generating units are paired with the N isolated DC / DC converters one by one and connected in the same way, that is, the positive terminal of the new energy generating unit is connected with the positive terminal of the generating side of the isolated DC / DC converter, and the negative terminal of the new energy generating unit is connected with the negative terminal of the generating side of the isolated DC / DC converter;

[0024] The N isolated DC / DC converters are paired with the N mechanical bypass switches one by one and connected in the same way, that is, the positive terminal of the collection side of the isolated DC / DC converter is connected with the positive terminal of the mechanical bypass switch, and the negative terminal of the collection side of the isolated DC / DC converter is connected with the negative terminal of the mechanical bypass switch;

[0025] The N isolated DC / DC converters are connected in series and connected with the collection converter, and the specific connection mode is that the positive terminal of the collection side of the first isolated DC / DC converter is connected with the positive terminal of the collection side of the collection converter, the negative terminal of the collection side of the Nth isolated DC / DC converter is connected with the negative terminal of the collection side of the collection converter, and the negative terminal of the collection side of the nth (n = 1, 2, 3, …, N-1) isolated DC / DC converter is connected with the positive terminal of the collection side of the (n+1)th isolated DC / DC converter;

[0026] Step two, control strategy

[0027] Step two, operation strategy of isolated DC / DC converter

[0028] The operation strategies of the N isolated DC / DC converters are the same, and are all the constant-power control with the voltage limiting of the collection side, and the power instruction of the ith (i = 1, 2, 3, …, N) isolated DC / DC converter is P i * The output power of the new energy power generation unit connected therewith is P 0i , the collection current is I, and the voltage limiting value of the collection side is U max , and the power instruction P i * The given method is:

[0029]

[0030] When the ith new energy power generation unit needs to be taken out of operation, that is, P 0i is 0, at this time, the power instruction P i * is given as 0, and the mechanical bypass switch is in the open state, and the mechanical bypass switch is in the closed state, and the mechanical bypass switch is in the closed state.

[0031] Step two, operation strategy of collection converter

[0032] The collection converter adopts the constant collection current I control, and controls the collection current I to satisfy:

[0033]

[0034] In the formula, Pma x is the power of the new energy power generation unit with the maximum output power;

[0035] Suppose that the total output power of all isolated DC / DC converters is P, then the power difference ΔP(k) of adjacent two control operations is defined as:

[0036] AP(k) = P(k) - P(k-1)

[0037] wherein P(k), P(k-1) are the total output power of all isolated DC / DC converters at the kth time and the (k-1)th time respectively;

[0038] Let the current command of the centralized converter for centralized side current control be I*, and the disturbance applied be C, then the given method of the current command I* is:

[0039]

[0040] wherein I*(k), I*(k-1) are the current command of the centralized converter for centralized side current control at the kth time and the (k-1)th time respectively;

[0041] Through the current command given method, when I≥Pma x / Uma x , a negative disturbance is applied to reduce I; when I≥Pma x / Uma x , a positive disturbance is applied to increase I, so that the new energy medium voltage DC centralized system based on adjustable DC voltage is finally stabilized at the working point of I=Pma x / Uma x , ensuring the MPPT operation of the new energy power generation unit and the minimum current stress operation under the MPPT operation.

[0042] Compared with the prior art, the present application has the following advantages:

[0043] 1. Compared with the existing fixed DC centralized voltage series centralized scheme, the present application makes the centralized transformer adopt fixed current control, so that the centralized voltage is automatically adjusted with the power of each wind turbine, realizing the MPPT operation of the entire centralized system, and effectively ensuring the power output capability of the new energy power plant.

[0044] 2. The centralized converter of the present application adopts constant current control and has a wide input voltage range, can adjust and optimize the current command according to the power, reduce the transformation ratio of the input and output voltage of the centralized converter, optimize the output voltage of the isolated DC / DC converter, and effectively improve the system operation efficiency and further improve the economy.

[0045] 3. Compared with the existing fixed DC centralized voltage series centralized scheme, the voltage regulation range required by the isolated DC / DC converter of the new energy power generation unit of the present application is smaller, the voltage gain is smaller, the design is easier, and low-voltage devices can be selected, so the cost is lower.

[0046] 4. Compared with the traditional parallel centralized scheme, the present application can save the number of expensive cables, reduce the cost and design difficulty of the isolated DC / DC converter, and has good economy.

[0047] 5、The application can automatically realize bypass when new energy generating unit needs to exit operation, has certain flexibility and fault tolerance ability. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 Structure schematic diagram of the new energy medium voltage DC collection system based on adjustable DC voltage provided by the application;

[0049] Figure 2 Operation strategy logic block diagram of the collection converter of the new energy medium voltage DC collection method based on adjustable DC voltage provided by the application;

[0050] Figure 3 Working point schematic diagram of the new energy medium voltage DC collection method based on adjustable DC voltage provided by the application;

[0051] Figure 4 Working point schematic diagram when the power P of the generating unit with the maximum output power of the new energy medium voltage DC collection method based on adjustable DC voltage provided by the application increases; max

[0052] Figure 5 Working point schematic diagram when the power P of the generating unit with the maximum output power of the new energy medium voltage DC collection method based on adjustable DC voltage provided by the application decreases; max

[0053] Figure 6 Working point schematic diagram when the power P of the generating unit with the non-maximum output power of the new energy medium voltage DC collection method based on adjustable DC voltage provided by the application changes; other

[0054] Figure 7 Structure schematic diagram of 5 wind turbines in series collection based on the new energy medium voltage DC collection system based on adjustable DC voltage provided by the application;

[0055] Figure 8 Main simulation working waveform of 5 wind turbines in series collection based on the new energy medium voltage DC collection method based on adjustable DC voltage provided by the application. DETAILED DESCRIPTION

[0056] The technical scheme of the application is further described below in combination with the drawings, but is not limited thereto, any modification or equivalent replacement to the technical scheme of the application without departing from the spirit and range of the technical scheme of the application should be covered in the protection range of the application.

[0057] The application provides a new energy medium voltage DC collection method based on adjustable DC voltage, which comprises the following steps: ​​​

[0058] Step one, design the topology structure of new energy medium voltage DC collection system based on adjustable DC voltage

[0059] As shown in Figure 1 The topology structure includes N new energy generating units, N isolated DC / DC converters, N mechanical bypass switches and a collection converter, wherein:

[0060] The N new energy generating units each contain a positive terminal and a negative terminal;

[0061] The N isolated DC / DC converters each contain a generating side and a collection side, wherein the generating side contains a positive terminal and a negative terminal, and the collection side contains a positive terminal and a negative terminal;

[0062] The N mechanical bypass switches each contain a positive terminal and a negative terminal;

[0063] The collection converter contains a collection side and a delivery side, wherein the collection side contains a positive terminal and a negative terminal, and the delivery side contains a positive terminal and a negative terminal;

[0064] The N new energy generating units are paired with the N isolated DC / DC converters in the same connection manner, that is, the positive terminal of the new energy generating unit is connected to the positive terminal of the generating side of the isolated DC / DC converter, and the negative terminal of the new energy generating unit is connected to the negative terminal of the generating side of the isolated DC / DC converter;

[0065] The N isolated DC / DC converters are paired with the N mechanical bypass switches in the same connection manner, that is, the positive terminal of the collection side of the isolated DC / DC converter is connected to the positive terminal of the mechanical bypass switch, and the negative terminal of the collection side of the isolated DC / DC converter is connected to the negative terminal of the mechanical bypass switch;

[0066] The N isolated DC / DC converters are connected in series and connected to the collection converter, and the specific connection manner is that the positive terminal of the collection side of the first isolated DC / DC converter is connected to the positive terminal of the collection side of the collection converter, the negative terminal of the collection side of the Nth isolated DC / DC converter is connected to the negative terminal of the collection side of the collection converter, and the negative terminal of the collection side of the nth (n=1, 2, 3, …, N-1) isolated DC / DC converter is connected to the positive terminal of the collection side of the n+1th isolated DC / DC converter.

[0067] In the present application, the positive terminal and the negative terminal of the delivery side of the collection converter can be used for new energy direct power supply application or new energy sending out.

[0068] In the present application, the collection converter can adopt a multi-port topology, so that a plurality of new energy generating unit series groups can be collected by using only one collection converter.

[0069] Step two, control strategy

[0070] The collection converter adopts constant current control, so that the collection voltage is automatically adjusted with the power of each fan, and the energy loss of any new energy power generation unit is avoided by reducing the collection voltage, thereby ensuring the MPPT operation of the entire system. Meanwhile, by optimizing the size of the collection voltage, the collection current is reduced as much as possible, so that the system realizes the minimum current stress operation under the MPPT operation. The specific control method is as follows:

[0071] Step two, operation strategy of isolated DC / DC converter

[0072] The operation strategy of the N isolated DC / DC converters is the same, and is constant power control with collection side voltage limiting. The power command of the i(i=1, 2, 3, …, N) isolated DC / DC converter is P i * The output power of the new energy power generation unit connected thereto is P 0i , the collection current is I, and the collection side voltage limiting value is U max , then the power command P i * The given method is as follows:

[0073]

[0074] The given method is to make the isolated DC / DC converter transmit all the power of the new energy power generation unit connected thereto to the next stage when the collection side voltage of the isolated DC / DC converter does not reach the limiting value, and transmit UmaxI power to the next stage when the collection side voltage of the isolated DC / DC converter reaches the limiting value. At this time, the new energy power generation unit will have residual power that cannot be transmitted to the rear stage and needs to be dissipated in the energy consumption circuit.

[0075] The scheme provided by the application can flexibly realize the operation of new energy power generation units. When the i-th new energy power generation unit needs to be taken out of operation, i.e. P0i is 0, according to formula (1), the power command P

[0076] Step two, operation strategy of isolated DC / DC converter

[0077] As shown in Figure 1 and 2 , the collection converter adopts constant collection current I control, and controls the collection current I to meet the following formula by applying current disturbance:

[0078]

[0079] Pma x is the power of the power generation unit with the maximum output power, Uma x is the voltage limiting value of the aggregation side of the isolated DC / DC converter.

[0080] Supposing that the total output power of all isolated DC / DC converters is P, the power difference ΔP(k) of adjacent two control operations can be defined as:

[0081] ΔP(k) = P(k) - P(k-1) (3)

[0082] wherein P(k) and P(k-1) are respectively the total output power of all isolated DC / DC converters at the kth time and the (k-1)th time.

[0083] Supposing that the current command of the aggregation converter for the aggregation side current control is I * , and the disturbance amount applied is C, the given method of the current command I * is:

[0084]

[0085] wherein I * (k) and I * (k-1) are respectively the current command of the aggregation converter for the aggregation side current control at the kth time and the (k-1)th time.

[0086] Through the current command given method, when I ≥ P max / U max , a negative disturbance is applied to reduce I; when I ≥ P max / U max , a positive disturbance is applied to increase I. Finally, the new energy medium voltage DC aggregation system based on the adjustable DC voltage can be stabilized at the working point of I = P max / U max , ensuring the MPPT operation of the new energy power generation unit and the minimum current stress operation under the MPPT operation.

[0087] The working point diagram of the new energy medium voltage DC aggregation method based on the adjustable DC voltage provided by the application is shown in Figure 3 , the working point diagram when the power P max of the power generation unit with the maximum output power increases is shown in Figure 4 , the working point diagram when the power P max of the power generation unit with the maximum output power decreases is shown in Figure 5 , and the working point diagram when the power P other of the power generation unit without the maximum output power changes is shown in Figure 6 .

[0088] In this invention, during the parameter design process, an appropriate current disturbance C can be selected based on factors such as steady-state current ripple, current response speed, and anti-interference capability.

[0089] The new energy medium-voltage DC collection method based on adjustable DC collection voltage proposed in this invention has advantages such as avoiding power loss, low design difficulty and cost of isolated DC / DC converters, low cable cost, low current stress, low voltage ratio of collection converter, and flexible switching. It has significant advantages over parallel DC collection and traditional series DC collection schemes with fixed collection voltage.

[0090] Example:

[0091] Using the above-mentioned new energy medium-voltage DC collection method based on adjustable DC voltage, five wind turbines are connected in series, such as... Figure 7 As shown. The wind turbine has a rated power of 5MW, the output voltage limit of the isolated DC / DC converter is 40kV, the rated collection voltage is 200kV, and the rated turbine cluster current is 125A. Wind turbine 1 initially has a power of 3MW and increases to 5MW at 2.5ms, while wind turbines 2, 3, 4, and 5 maintain a power of 3MW. The main simulation waveforms of the new energy medium-voltage DC collection scheme based on adjustable DC collection voltage proposed in this invention are shown below. Figure 8 As shown.

[0092] Phase 1 (t0~t1): During this phase, |ΔP|≥U is always satisfied. max C / 2 Current Command I * A positive disturbance is continuously applied, causing the collector current I to rise from 0 to P. max / U max =75A, the total output power P of the wind turbine cluster also increases from 0 to the total power of all wind turbines, reaching 15MW. During this period, I is less than P. max / U max The collector voltage of each isolated DC / DC converter is at the limit of 40kV, and the collector voltage U cluster The rated value is 200kV.

[0093] Phase 2 (t1~t2): During this phase, the system's |ΔP| continuously exceeds or equals U. max C / 2 and less than U max Switching between C / 2, current command I * Alternating positive and negative disturbances are applied to keep I essentially constant at 75 Å, P essentially constant at 15 MW, and U... cluster Maintaining a constant voltage of 200kV, the entire system achieves MPPT operation, meaning no wind curtailment, while simultaneously achieving minimum current stress operation under no wind curtailment conditions.

[0094] Work stage three: (t2~t3), because the fan 1 power suddenly increases to 5MW at t3, while the power of other fans remains 3MW, the power of each fan is unbalanced, in order to keep the operation without "abandoned wind", the system gathers voltage U cluster From the rated value, while I increases to the current P max / U max =125A, P increases to the current total fan power and 17MW.

[0095] Work stage four: (t3~t4), this stage is similar to stage two, I basically remains unchanged at 125A, P basically remains unchanged at 17MW, U cluster Remain below the rated value operation, the voltage ratio of the gathering side of each isolated DC / DC converter is equal to the fan power ratio, where the gathering side voltage of the isolated DC / DC converter of the fan with the largest power is the limiting value, that is, the system still realizes the minimum current stress operation without "abandoned wind".

Claims

1. A new energy medium voltage direct current collection method based on adjustable direct current voltage, characterized in that The method comprises the following steps: Step one, design the topology structure of new energy medium voltage DC collection system based on adjustable DC voltage The topology of the system comprises a new energy power generation unit, an isolated DC / DC converter, a mechanical bypass switch and a collection converter, wherein: The Each new energy power generation unit comprises a positive terminal and a negative terminal. The Each isolated DC / DC converter comprises a power generation side and a collection side, wherein the power generation side comprises a positive terminal and a negative terminal, and the collection side comprises a positive terminal and a negative terminal. The Each mechanical bypass switch includes a positive terminal and a negative terminal. The collection converter comprises a collection side and a delivery side, wherein the collection side comprises a positive terminal and a negative terminal, and the delivery side comprises a positive terminal and a negative terminal; The Each new energy power generation unit and Each isolated DC / DC converter is paired with the other and connected in the same way: the positive terminal of the new energy power generation unit is connected to the positive terminal of the power generation side of the isolated DC / DC converter, and the negative terminal of the new energy power generation unit is connected to the negative terminal of the power generation side of the isolated DC / DC converter. The Isolated DC / DC converters are paired with Mechanical bypass switches in the same way, that is, the positive terminal of the isolated DC / DC converter on the collection side is connected to the positive terminal of the mechanical bypass switch, and the negative terminal of the isolated DC / DC converter on the collection side is connected to the negative terminal of the mechanical bypass switch. The first isolated DC / DC converter is connected in series with the collection converter, and the specific connection mode is that the positive terminal of the collection side of the first isolated DC / DC converter is connected with the positive terminal of the collection side of the collection converter, the negative terminal of the collection side of the first isolated DC / DC converter is connected with the negative terminal of the collection side of the collection converter, the negative terminal of the collection side of the second isolated DC / DC converter is connected with the positive terminal of the collection side of the collection converter, and the positive terminal of the collection side of the second isolated DC / DC converter is connected with the negative terminal of the collection side of the collection converter. The first isolated DC / DC converter is connected in series with the collection converter, and the specific connection mode is that the positive terminal of the collection side of the first isolated DC / DC converter is connected with the positive terminal of the collection side of the collection converter, the negative terminal of the collection side of the first isolated DC / DC converter is connected with the negative terminal of the collection side of the collection converter, the negative terminal of the collection side of the second isolated DC / DC converter is connected with the positive terminal of the collection side of the collection converter, and the positive terminal of the collection side of the second isolated DC / DC converter is connected with the negative terminal of the collection side of the collection converter. The first isolated DC / DC converter is connected in series with the collection converter, Step two, operation strategy of isolated DC / DC converter The operation strategies of the isolated DC / DC converters are the same, and are all constant-power control with voltage limiting of the collection side. Assuming that the power instruction of the nth isolated DC / DC converter is , the output power of the new energy power generation unit connected to the nth isolated DC / DC converter is , the collection current is , and the voltage limiting value of the collection side is , the power instruction is given by the following method: ​​ When the Each new energy power generation unit needs to be taken out of operation, that is... When it is 0, the power command is... Given a value of 0, a zero-voltage condition is provided for the corresponding mechanical bypass switch. This can be achieved by directly setting the mechanical bypass switch to the open state. Similarly, when the first... When a new energy power generation unit needs to be put into operation, the corresponding mechanical bypass switch should be closed first. Step three, operation strategy of collection converter The current collector converter employs a fixed current collection current The control, and the control of the current collection current by means of the application of current perturbations satisfies: In the formula is the power of the new energy power generation unit with the maximum output power; Let the total output power of all isolated DC / DC converters be The power difference between two adjacent control operations is defined as: ​ In the formula , The first Second and third The total output power of all isolated DC / DC converters; Let the current instruction of the current control of the set converter fixed set side be , the disturbance amount applied is , and the given method of the current instruction is: In the formula , are the first and second aggregate converter current commands, respectively, for controlling the aggregate side current of the converter; and are the first and second aggregate converter current commands, respectively, for controlling the aggregate side current of the converter.​ By the current command giving method, the negative disturbance is applied at the time, and the ; positive disturbance is applied at the time, and the is increased, and finally the new energy medium voltage DC collection system based on the adjustable DC voltage is stabilized at the working point of , the MPPT operation of the new energy power generation unit and the minimum current stress operation under the MPPT operation are ensured.

2. The new energy medium voltage DC collection method based on adjustable DC voltage according to claim 1, characterized in that The positive terminal and the negative terminal of the delivery side of the collection converter are used for new energy direct power supply application or new energy sending out.

3. The adjustable DC voltage-based new energy medium voltage DC collection method according to claim 1, characterized in that The collection converter adopts a multi-port topology to complete the collection of multiple new energy generation unit series groups with only one collection converter.

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