CN103277252B - Control method of grid connected wind turbine - Google Patents

Abstract

The invention relates to a control method of a grid connected wind turbine. An impeller of the grid connected wind turbine captures wind energy, converts the wind energy into mechanical energy, and transmits the mechanical energy to a power generator, and the power generator outputs power to a power grid. Before grid connection of the power generator, a controller adjusts the discharge volume of a volume-adjustable hydraulic pump to the maximum value a, adjusts the discharge volume of a volume-adjustable hydraulic motor, and controls the rotation speed of the power generator to reach a grid-connection rotation speed. After grid connection of the power generator, when the controller detects that the wind speed rises, the controller adjusts the discharge volume of the volume-adjustable hydraulic pump to zero, and adjusts the discharge volume of the volume-adjustable hydraulic motor, so that the rotation speed of the impeller reaches the best rotation speed, and the maximum power tracking control is controlled. When the controller detects that the wind speed decreases, the controller adjusts the discharge volume of the volume-adjustable hydraulic motor to zero, and adjusts the discharge volume of the volume-adjustable hydraulic pump, so that the rotation speed of the impeller reaches the best rotation speed, and the maximum power tracking control is achieved. The control method of the grid connected wind turbine can not only efficiently transmit energy, but also relieve the torque ripple of a transmission system, improves the energy utilization rate, and meanwhile lowers the fault rate of the transmission system.

Description

A method for controlling a grid-connected wind turbine

technical field

The invention belongs to the field of wind power generation, and in particular relates to a control method for a grid-connected wind power machine.

Background technique

With the increase of large-scale wind turbines and the promotion of offshore wind power, changes in the operating environment and working conditions of wind turbines have made the transmission components such as gearboxes and main shafts suffer from more severe fluctuations in speed and torque, and the cost of fault maintenance has increased significantly. Statistics show that the transmission failure cost of wind turbine gearbox accounts for more than 60% of the maintenance cost of the unit, and the high incidence period of gearbox failure occurs in the 5-8 years after the wind turbine is put into operation, which is different from the design life of the wind turbine of 15-20 years. There is a clear gap. Under the current design and manufacturing level, the operational reliability of the wind turbine gearbox has become one of the bottleneck issues affecting the life cycle of the complete machine and the sustainable development of the wind power industry.

In wind power generation technology, variable speed and constant frequency technology can make the impeller run at variable speed, and maintain a nearly constant optimal tip speed ratio in a wide range of wind speeds, thereby improving the operating efficiency of the wind turbine. Energy can be much higher than constant speed wind turbines. However, for wind turbines driven by gearboxes, the variable speed and constant frequency operation of grid-connected wind turbines is controlled by power electronic equipment. The use of power electronic equipment increases the cost of equipment; Due to the inertia of the mechanical transmission system, the use of variable speed and constant frequency technology to adjust the impeller speed will lag in time, which prolongs the time of the impeller speed change process, which is not conducive to improving energy utilization. In addition, due to the instability of wind speed, mechanical transmission will generate large impact loads and vibrations, which will have a large impact on generators and power grids.

Contents of the invention

The technical problem to be solved by the present invention is to provide a grid-connected wind turbine control method, which uses a mechanical-hydraulic hybrid transmission device to control the variable speed and constant frequency operation of the wind turbine, reduces the torque fluctuations on the mechanical structure, and shortens the speed change time of the impeller , improve energy utilization.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

A control method for a grid-connected wind turbine. The impeller of the grid-connected wind turbine captures wind energy and converts it into mechanical energy. The impeller rotates under the action of the wind and drives the speed-up planetary gear to rotate. The hydraulic hybrid transmission transfers energy to a generator, which outputs electricity to the grid. The mechanical-hydraulic hybrid transmission device includes a first gear, a first gear pair, a second gear pair, a speed-regulating planetary gear and a speed-regulating hydraulic system, and the first gear is coupled with the output shaft of the speed-up planetary gear. The second gear pair includes a fifth gear and a sixth gear meshed with each other, and one end of the fifth gear is coupled with the generator. The speed regulating hydraulic system includes a variable hydraulic pump, a variable hydraulic motor, an accumulator and an oil tank.

Before the generator is connected to the grid, the controller outputs a displacement control signal of the variable hydraulic pump to the displacement actuator of the variable hydraulic pump to adjust the displacement of the variable hydraulic pump to a maximum value a. The controller collects the generator speed signal transmitted by the first speed sensor installed at the input shaft of the generator. The controller calculates and outputs the variable hydraulic motor displacement control signal to the displacement actuator of the variable hydraulic motor according to the generator speed ω _e to adjust the displacement of the variable hydraulic motor and control the power generation The speed ω _e of the machine reaches the grid-connected speed. At this point, the generator is connected to the grid.

After the generator is connected to the grid, the controller collects the wind speed signal transmitted by the wind speed sensor installed at the impeller, and collects the impeller speed signal transmitted by the second speed sensor installed at the output shaft of the impeller. Each wind speed v corresponds to an optimum impeller speed ω _opt such that the impeller captures the maximum power. Under different wind speed characteristics, the controller will perform the following control process:

1) When the controller detects that the wind speed is rising, the controller outputs a displacement control signal of the variable hydraulic pump to the displacement actuator of the variable hydraulic pump to adjust the displacement of the variable hydraulic pump to zero.

The controller calculates the optimal impeller speed ω _opt under the current wind speed v according to the optimal tip speed ratio λ _opt , and compares it with the current impeller speed ω collected by the second speed sensor, and calculates the theoretical value of the variable hydraulic motor Displacement D _m , and transmit the theoretical displacement D _m signal to the displacement actuator of the variable hydraulic motor to adjust the displacement of the variable hydraulic motor so that the speed of the impeller reaches the optimum impeller speed ω _opt . Therefore, by adjusting the displacement of the variable hydraulic motor, the impeller runs at the optimum impeller speed ω _opt to realize the maximum power tracking control.

2) When the controller detects that the wind speed drops, the controller outputs a displacement control signal of the variable hydraulic motor to the displacement actuator of the variable hydraulic motor to adjust the displacement of the variable hydraulic motor to zero.

The controller calculates the optimal impeller speed ω _opt under the current wind speed v according to the optimal tip speed ratio λ _opt , and compares it with the current impeller speed ω collected by the second speed sensor, and calculates the theoretical value of the variable hydraulic pump Displacement D _p , and transmit the theoretical displacement D _p signal to the displacement actuator of the variable hydraulic pump to adjust the displacement of the variable hydraulic pump so that the speed of the impeller reaches the optimum impeller speed ω _opt . Therefore, by adjusting the displacement of the variable hydraulic pump, the impeller runs at the optimum impeller speed ω _opt to realize the maximum power tracking control.

Further, the speed-regulating planetary gear includes a ring gear, a planetary gear, a sun gear, a planet carrier and a second gear, the second gear meshes with the first gear, and the output shaft of the ring gear is connected to the The other end of the fifth gear is connected. The first gear pair includes a meshing third gear and a fourth gear, the third gear is coupled with the sun gear, the fourth gear is coupled with the input shaft of the variable displacement hydraulic pump, and the The output shaft of the variable hydraulic motor is connected with the sixth gear.

Further, the planetary gears mesh with the ring gear and the sun gear respectively, and the planetary gears are installed on the planetary carrier and can rotate around it. The planet carrier is fixedly coupled with the second gear, and the planet carrier and the second gear can rotate around the coupling shaft of the sun gear and the third gear.

Further, the accumulator is connected to the pipeline where the output port of the variable hydraulic pump is connected to the input port of the variable hydraulic motor, and the input port of the variable hydraulic pump is connected to the output port of the variable hydraulic motor. are connected to the fuel tank.

Further, the speed regulating hydraulic system also includes a one-way valve, a shut-off valve, an overflow valve and an oil filter. The one-way valve is installed between the variable hydraulic pump and the variable hydraulic motor, the cut-off valve is installed at the outlet of the accumulator, the overflow valve is connected to the inlet of the variable hydraulic motor, and the oil filter The device is installed at the outlet and inlet of the fuel tank.

Adopt the present invention to have following beneficial effect:

1. It can control the wind turbine to run in the variable speed and constant frequency working mode, which improves energy utilization and facilitates grid-connected operation.

2. The flexible characteristics of the speed-regulating hydraulic system can reduce the torque fluctuation of the transmission system; at the same time, under different wind conditions (wind speed rises/falls), it is easier to control the wind turbine by using the method of variable displacement hydraulic pump and variable hydraulic motor. Quickly enter the working mode of variable speed and constant frequency.

3. It still has the characteristics of high transmission efficiency of mechanical transmission, so that the overall mechanical-hydraulic hybrid transmission efficiency is maintained at a high level.

Description of drawings

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

1 is a schematic diagram of the working principle of a wind turbine using a grid-connected wind turbine control method of the present invention;

Fig. 2 is the relationship curve of impeller capture power-rotational speed under different wind speeds.

Detailed ways

Figure 1 is a schematic diagram of the working principle of a grid-connected wind turbine using a control method for a grid-connected wind turbine according to the present invention. Transmission device 4 and controller 6. The impeller 1 captures wind energy and converts it into mechanical energy. The impeller 1 rotates under the action of the wind and drives the speed-up planetary gear 2 to rotate. The speed-up planetary gear 2 transmits energy to the generator through the mechanical-hydraulic hybrid transmission 4 3. The generator 3 outputs electric energy to the grid.

The mechanical-hydraulic hybrid transmission device 4 includes a first gear 41 , a first gear pair 42 , a second gear pair 43 , speed-regulating planetary gears and a speed-regulating hydraulic system 5 . The first gear 41 is coupled with the output shaft of the speed-up planetary gear 2 . The first gear pair 42 includes a meshed third gear 421 and a fourth gear 422, the second gear pair 43 includes a meshed fifth gear 431 and a sixth gear 432, and the speed-regulating planetary gear includes teeth ring 71 , planetary gear 72 , sun gear 73 , planetary carrier 74 and second gear 75 .

The planetary gear 72 meshes with the ring gear 71 and the sun gear 73 respectively, and the planetary gear 72 is installed on the planetary carrier 74 and can rotate around it. The planet carrier 74 is fixedly coupled with the second gear 75 , and the planet carrier 74 and the second gear 75 can rotate around the coupling shaft of the sun gear 73 and the third gear 421 . The first gear 41 is meshed with the second gear 75, one end of the fifth gear 431 is connected with the generator 3, and the other end of the fifth gear 431 is connected with the output of the ring gear 71. Axes are connected.

The speed regulating hydraulic system 5 includes a variable hydraulic pump 51 , a variable hydraulic motor 52 , a one-way valve 53 , an accumulator 54 , a stop valve 55 , an overflow valve 56 , an oil tank 57 and an oil filter 58 . The output port of the variable hydraulic pump 51 is connected to the input port of the one-way valve 53 , and the output port of the one-way valve 53 is connected to the input port of the variable hydraulic motor 52 . One end of the stop valve 55 is connected to the accumulator 54 , and the other end of the stop valve 55 is connected to the pipeline connecting the one-way valve 53 and the variable hydraulic motor 52 . The input port of the variable hydraulic pump 51 and the output port of the variable hydraulic motor 52 are both connected to the oil tank 57 , and the oil filter 58 is installed at the inlet and outlet of the oil tank 57 . The overflow valve 56 is connected with the inlet of the variable hydraulic motor 52 .

The third gear 421 is connected with the sun gear 73 , the fourth gear 422 is connected with the input shaft of the variable hydraulic pump 51 , and the output shaft of the variable hydraulic motor 52 is connected with the sixth gear 432 .

A wind speed sensor 82 is installed at the impeller for detecting wind speed. A second rotational speed sensor 83 is installed at the output shaft of the impeller for detecting the rotational speed of the impeller. A first rotational speed sensor 81 is installed at the input shaft of the generator for detecting the rotational speed of the generator. The first rotational speed sensor 81 , the wind speed sensor 82 , the second rotational speed sensor 83 , the displacement actuators of the variable hydraulic pump 51 and the displacement actuators of the variable hydraulic motor 52 are respectively electrically connected to the controller 6 .

Next, with reference to FIG. 2 , the variable speed constant frequency control theory of the wind turbine, that is, the maximum power tracking control of the impeller 1 is described.

According to the Betz theory, the power captured by the wind turbine's impeller from the wind is:

In the formula, P is the capture power of the impeller, ρ is the air density, S is the swept area of the impeller, v is the wind speed, and C _p is the energy capture coefficient.

As shown in Figure 2, the relationship curve between impeller 1 capture power P and impeller speed ω under different wind speeds (such as V ₁ -V ₄ ), corresponding to each wind speed, there is a maximum power point (points A, B, C, D ), the maximum power curve of impeller 1 can be obtained by connecting the maximum power points of these curves.

At each point of the maximum power curve, the change in power captured by impeller 1 relative to the change in impeller speed ω is zero, at which point the impeller captures maximum power, namely:

It can be known from the above formula that by adjusting the impeller speed ω, the impeller 1 can capture the maximum power.

In conjunction with Fig. 2 and the variable speed constant frequency control theory of the wind turbine, the control method of a grid-connected wind turbine according to the present invention is as follows:

Before the generator 3 is connected to the grid, the controller 6 outputs a displacement control signal of the variable hydraulic pump 51 to the displacement actuator of the variable hydraulic pump 51 to adjust the displacement of the variable hydraulic pump 51 to the maximum value a. The controller 6 collects the rotation speed signal of the generator 3 transmitted from the first rotation speed sensor 81 installed at the input shaft of the generator 3 . The controller 6 calculates and outputs the displacement control signal of the variable hydraulic motor 52 to the displacement actuator of the variable hydraulic motor 52 according to the magnitude of the rotational speed ω _e of the generator 3 to adjust the displacement of the variable hydraulic motor 52 , controlling the speed ω _e of the generator 3 to reach the grid-connected speed. At this time, the generator 3 is connected to the grid. This process is a wind turbine constant frequency control process.

After the generator 3 is connected to the grid, the controller 6 collects the wind speed signal transmitted by the wind speed sensor 82 installed at the impeller 1, and collects the wind speed signal transmitted by the second speed sensor 83 installed at the output shaft of the impeller 1. The incoming impeller speed signal. Each wind speed v corresponds to an optimum impeller speed ω _opt , enabling said impeller 1 to capture maximum power. Under different wind speed characteristics, the controller 6 will perform the following control process:

1) When the wind speed rise is detected, the controller 6 outputs a displacement control signal of the variable hydraulic pump 51 to the displacement actuator of the variable hydraulic pump 51 to adjust the displacement of the variable hydraulic pump 51 to zero.

The controller 6 calculates the optimal impeller speed ω _opt at the current wind speed v according to the optimal tip speed ratio λ _opt , and compares it with the current impeller speed ω collected by the second speed sensor 83 to calculate the variable hydraulic motor 52 theoretical displacement D _m , and transmit the theoretical displacement D _m signal to the displacement actuator of the variable hydraulic motor 52 to adjust the displacement of the variable hydraulic motor 52 so that the speed of the impeller 1 reaches the optimum impeller speed ω _opt . Therefore, by adjusting the displacement of the variable hydraulic motor 52, the impeller 1 operates at the optimum impeller speed ω _opt to realize maximum power tracking control.

The above control process 1) is described in Figure 2 as follows: Suppose the wind turbine runs at point B, and the impeller captures the maximum power at the wind speed _V2 . If the wind speed suddenly rises from V ₂ to V ₁ , the wind turbine will run at point F, but due to the inertia of the impeller and the transmission system, it will take a while for the impeller speed to rise from point F to point A. In order to shorten the time for the impeller speed to rise from point F to point A, the displacement of the variable hydraulic pump 51 is adjusted to zero, and by adjusting the displacement of the variable hydraulic motor 52, the energy stored in the accumulator 54 passes through the variable hydraulic motor 52 Release it, make the variable hydraulic motor 52 work on the generator 3, reduce the impeller load with this, and make the impeller speed rise to the working state of point A quickly. As a result, the speed change time of the impeller 1 is shortened when the wind speed rises, and the maximum power capture state can be reached as quickly as possible.

2) When the wind speed drops, the controller 6 outputs a displacement control signal of the variable hydraulic motor 52 to the displacement actuator of the variable hydraulic motor 52 to adjust the displacement of the variable hydraulic motor 52 to zero.

The controller 6 calculates the optimal impeller speed ω _opt at the current wind speed v according to the optimal tip speed ratio λ _opt , and compares it with the current impeller speed ω collected by the second speed sensor 83 to calculate the variable hydraulic pump 51 theoretical displacement D _p , and transmit the theoretical displacement D _p signal to the displacement actuator of variable hydraulic pump 51 to adjust the displacement of variable hydraulic pump 51 so that the speed of impeller 1 reaches the optimum impeller speed ω _opt . Therefore, by adjusting the displacement of the variable hydraulic pump 51, the impeller 1 operates at the optimum impeller speed ω _opt to realize the maximum power tracking control.

The above control process 2) is described in Fig. 2 as follows: Assume that the wind turbine operates at point C, and the impeller captures the maximum power at the wind speed V ₃ . If the wind speed suddenly drops from V ₃ to V ₄ , the wind turbine will run at point E, but due to the inertia of the impeller and the transmission system, it will take a while for the impeller speed to drop from point E to point D. In order to shorten the time for the impeller speed to drop from point E to point D, the displacement of the variable hydraulic motor 52 is adjusted to zero, and by adjusting the displacement of the variable hydraulic pump 51, the impeller acts on the variable hydraulic pump 51, and the variable hydraulic pump 51 The output energy is temporarily stored in the accumulator 54, so as to increase the load of the impeller, so that the rotating speed of the impeller rapidly drops to the working state at point D. Therefore, the speed change time of the impeller 1 is shortened when the wind speed drops, and the maximum power capture state can be reached as quickly as possible.

3) When the wind speed is constant, the controller 6 outputs a displacement control signal to the displacement actuator of the variable hydraulic pump 51 and the displacement actuator of the variable hydraulic motor 52, and the displacement of the variable hydraulic pump 51 and The displacements of the variable hydraulic motors 52 are all adjusted to zero. At this point, the impeller will continuously capture maximum power.

A grid-connected wind turbine control method in the present invention is mainly realized by controlling the mechanical-hydraulic hybrid transmission device 4 . The mechanical-hydraulic hybrid transmission device 4 is a combination of a mechanical transmission device and a hydraulic transmission device. The mechanical-hydraulic hybrid transmission device 4 integrates the high efficiency of the mechanical transmission device and the flexibility of the hydraulic transmission device. In the wind energy captured by the grid-connected wind turbine, most of the energy is transmitted to the generator through the mechanical transmission part, and a small part of the energy is transmitted to the generator through the hydraulic transmission part. When the variable-speed and constant-frequency operation of the grid-connected wind turbine is realized by controlling the mechanical-hydraulic hybrid transmission device 4, the accumulator 54 in the speed-adjusting hydraulic system 5 can partially absorb the torque mutation caused by wind speed fluctuations, avoiding damage to the mechanical transmission part. Larger impact reduces the failure rate of mechanical transmission parts.

Claims (5)

1. a grid-connected wind machine controlling method, impeller (1) capturing wind energy of this grid-connected wind machine is also translated into mechanical energy, impeller (1) rotates and drives speedup planetary pinion (2) to rotate under wind action, described speedup planetary pinion (2) by mechanical-hydraulic hybrid transmission (4) by energy transferring to generator (3), generator (3) export electric energy to electrical network; Described mechanical-hydraulic hybrid transmission (4) comprises the first gear (41), the first gear pair (42), the second gear pair (43), speed governing planetary pinion and speed-regulating hydraulic system (5), and described first gear (41) is connected with the output shaft of described speedup planetary pinion (2); Described second gear pair (43) comprises the 5th gear (431) and the 6th gear (432) that are meshed, and one end and the described generator (3) of described 5th gear (431) are connected; Described speed-regulating hydraulic system (5) comprises volume adjustable hydraulic pump (51), variable hydraulic motor (52), accumulator (54) and fuel tank (57); It is characterized in that:

Before described generator (3) is grid-connected, controller (6) output variable oil hydraulic pump (51) displacement control signal gives the discharge capacity actuator of described volume adjustable hydraulic pump (51), and the discharge capacity of described volume adjustable hydraulic pump (51) is adjusted to maximum value a; Generator (3) tach signal that the first speed probe (81) transmission that described controller (6) collection is arranged on generator (3) input shaft place is come; Described controller (6) is according to generator (3) rotational speed omega _esize, calculate and output variable oil hydraulic motor (52) displacement control signal to the discharge capacity actuator of described variable hydraulic motor (52), regulate the discharge capacity of described variable hydraulic motor (52), control the rotational speed omega of described generator (3) _ereach grid-connected rotating speed; Now, described generator (3) is connected to the grid;

After described generator (3) is grid-connected, the wind velocity signal that air velocity transducer (82) transmission that described controller (6) collection is arranged on described impeller (1) place is come, and the wheel speed signal that the second speed probe (83) transmission that collection is arranged on described impeller (1) output shaft place is come; Each wind speed van all corresponding best wheel speed ω _opt, make described impeller (1) capture peak output; Under different wind speed characteristics, described controller (6) will perform following control procedure:

1) when described controller (6) detects that wind speed rises, controller (6) output variable oil hydraulic pump (51) displacement control signal gives the discharge capacity actuator of described volume adjustable hydraulic pump (51), and the discharge capacity of described volume adjustable hydraulic pump (51) is adjusted to zero;

Described controller (6) is according to optimum tip-speed ratio λ _optcalculate current wind speed vunder best wheel speed ω _opt, and contrast with the wheel speed ω that current second speed probe (83) collects, calculate the Theoretical flowing capacity D of described variable hydraulic motor (52) _m, and by this Theoretical flowing capacity D _msignal transmission is to the discharge capacity actuator of variable hydraulic motor (52), and the discharge capacity of Moderator Variable oil hydraulic motor (52), makes the rotating speed of impeller (1) reach best wheel speed ω _opt; Thus make impeller (1) operate at best wheel speed ω by the discharge capacity of Moderator Variable oil hydraulic motor (52) _opt, realize maximal power tracing and control;

2) when described controller (6) detects wind speed decreased, controller (6) output variable oil hydraulic motor (52) displacement control signal gives the discharge capacity actuator of described variable hydraulic motor (52), and the discharge capacity of described variable hydraulic motor (52) is adjusted to zero;

Described controller (6) is according to optimum tip-speed ratio λ _optcalculate current wind speed vunder best wheel speed ω _opt, and contrast with the wheel speed ω that current second speed probe (83) collects, calculate the Theoretical flowing capacity D of described volume adjustable hydraulic pump (51) _p, and by this Theoretical flowing capacity D _psignal transmission is to the discharge capacity actuator of volume adjustable hydraulic pump (51), and the discharge capacity of Moderator Variable oil hydraulic pump (51), makes the rotating speed of impeller (1) reach best wheel speed ω _opt; Thus make impeller (1) operate at best wheel speed ω by the discharge capacity of Moderator Variable oil hydraulic pump (51) _opt, realize maximal power tracing and control.

2. according to a kind of grid-connected wind machine controlling method according to claim 1, it is characterized in that: described speed governing planetary pinion comprises gear ring (71), planet wheel (72), sun gear (73), planet carrier (74) and the second gear (75), described second gear (75) is meshed with described first gear (41), and the output shaft of described gear ring (71) and the other end of described 5th gear (431) are connected; Described first gear pair (42) comprises the 3rd gear (421) and the 4th gear (422) that are meshed, described 3rd gear (421) and described sun gear (73) are connected, described 4th gear (422) is connected with the input shaft of described volume adjustable hydraulic pump (51), and the output shaft of described variable hydraulic motor (52) is connected with the 6th gear (432).

3. according to a kind of grid-connected wind machine controlling method according to claim 2, it is characterized in that: described planet wheel (72) is meshed with gear ring (71) and sun gear (73) respectively, described planet wheel (72) is arranged on planet carrier (74) and above also can rotates around it; Described planet carrier (74) and described second gear (75) are fixedly connected, and described planet carrier (74) and described second gear (75) can rotate around the joining shaft of described sun gear (73) and described 3rd gear (421).

4. according to a kind of grid-connected wind machine controlling method described in Claims 2 or 3, it is characterized in that: on the pipeline that the delivery outlet that described accumulator (54) is connected to described volume adjustable hydraulic pump (51) is connected with the inlet opening of described variable hydraulic motor (52), the inlet opening of described volume adjustable hydraulic pump (51) is all connected with described fuel tank (57) with the delivery outlet of described variable hydraulic motor (52).

5. according to a kind of grid-connected wind machine controlling method according to claim 4, it is characterized in that: described speed-regulating hydraulic system (5) also comprises one-way valve (53), stop valve (55), relief valve (56) and oil purifier (58); Described one-way valve (53) is arranged between volume adjustable hydraulic pump (51) and variable hydraulic motor (52), described stop valve (55) is arranged on the outlet port of accumulator (54), described relief valve (56) is connected with the entrance of described variable hydraulic motor (52), and described oil purifier (58) is arranged on the entry and exit place of fuel tank (57).